I wrote out the following for someone else a while ago when they had a similar question. I’ll recopy it here:

In general the Deck is pretty straightforward. SteamOS feels natural to use on the device, so it's a simple matter of booting it up, installing a game, and jumping in to play. There are not a lot of barriers, which is great! If you've been out of gaming for a while, this is absolutely what I'd recommend.

Your Deck will have a Great on Deck section of your library which has a list of "Verified" games that you own, designated by a green check mark. These are games that Valve has rated as running perfectly on the Deck and should Just Work™ without any tinkering or effort needed. If you stick to those, your experience should be pretty frictionless. You can also browse the store the same way, to easily see which games are Deck-friendly to buy.

Now, with that said, you can also go pretty deep with the device. It's simultaneously very casual-friendly but also very power-user-friendly. So, what follows is a bit more power-user stuff. None of this is essential information at all. You can absolutely enjoy hundreds of hours on the Deck without even touching anything I mention below, but a lot of it is good to know or at least have in your back pocket.

Also, if you have ANY questions, please ask! I'm happy to help out as best as I can, as I'm sure are many others. Us Deckers tend to have a bit of a cult-like affinity for the device (my friends have already told me to stop mentioning that it's on sale 😂).

Aperture Desk Job

The Deck comes with its own orientation game: Aperture Desk Job. Play it! It's fun. It takes about half an hour to complete. It's full of all the same humor and imagination as the games that Valve makes used to make.

Power adapter and cord

I tend to play plugged in most of the time, and the built in power adapter covered both outlets I would normally use and had a shorter cord than I would have liked. I replaced the power adapter with an Anker Nano 2 and a longer USB-C cable (make sure it's capable of power delivery). The Nano 2 is small enough that it doesn't cover the outlet next to it, so I can use that for something else (usually my phone/headphones).

Bluetooth headphones

Once paired, bluetooth headphones don't automatically connect to Steam Deck when turned on (no idea why). Each time you use them, you have to go into the Bluetooth menu under Settings and manually activate them.

Joystick caps

This is entirely personal preference, but the default thumbsticks were too smooth for me. My thumbs would slip off of them. I bought some silicone joystick caps to go over the tops of them and now find them much more pleasant to use. One caveat is that the Deck's joysticks are touch-sensitive and can be used to activate things like gyro controls, and putting caps on them means you lose out on that. I don't use the touch-sensitive feature myself so it's no big loss for me, and if I ever did need to, the caps are easy enough to remove temporarily. I'd wait until you get it to see if you need these though. For contrast, my husband doesn't use them at all and is fine with the default sticks. It's very much a personal preference thing.

Steam Deck button shortcuts

Occasionally you'll run into a situation where default controller input isn't sufficient. A game might want you to type in your character name with a keyboard, or maybe there's a launcher that's asking you to configure your graphics settings before you fully open the game.

Steam has these options built right into the Deck. The ones I use most are the keyboard STEAM + X, and forcing a mouse STEAM + RIGHT TRACKPAD to move and STEAM + R2 to click. You can also click on the trackpad (but I find it awkward), and you can also usually click on the screen itself (since it's touch-sensitive).

If a game hangs or crashes, STEAM + B force exits the game. You can also press the STEAM button to pull up a menu of options and exit the game that way.

Steam Input

This is the secret sauce of the Steam Deck, and one of the reasons why I think it's superior to any competitor. Steam Input is an entire framework that lets you create and share customizable control sets for any game. Most games on the Steam Deck just work with default controls, but for the ones that don't, you can either create your own or download a community-made profile.

For example, one of the first things I did with my Deck was I used Steam Input to bind the A button in Vampire Survivors to one of the back left paddle buttons. That meant that I could play the game one-handed, using the left joystick to move and the left back paddle to select my choices. I would wake up on the weekend, boot up the game, and play it with one hand while sipping coffee with my other. It was amazing.

Steam Input will even work on non-Steam games, so if you ever add any extra games or emulate anything, you can use it to get the controls exactly how you want. The framework is incredibly deep and includes things like chorded inputs and automatic rapidfire-button presses (AKA "turbo" mode). It's very valuable for accessibility as well, should you have any needs in that area.

ProtonDB

As I mentioned above, Valve has its own built-in game rating system for how well a game will theoretically run on the Deck. Here's the rundown of the four ratings a game can have:

1. Verified (should run perfectly)
2. Playable (runs, but with some caveats)
3. Unknown (Valve hasn't yet rated the game)
4. Unsupported (shouldn't run)

Sticking to Verified and Playable games is the easiest. The difference between the two is that a Playable game might have text that's a bit too small to read comfortably on the Deck, or it might require keyboard input at some point (so you'd have to use the keyboard hotkey).

Now, with tens of thousands of games on Steam, and with games changing and being updated all the time, it's also possible that sometimes these ratings are off. Sometimes a Verified game has issues, and sometimes an Unsupported game actually works perfectly.

Also, it's possible you have a lot of games in your library that you'd like to play, but they have an Unknown rating. All of these situations are where ProtonDB comes in. It's a community database of reports for how individual games run on Linux in general, and on the Steam Deck in particular. Here's the page for Grand Theft Auto 5, for example, where you can see reports specifically for the Steam Deck. ProtonDB will let you know whether or not a game runs and, in cases where it doesn't, will sometimes give you manual steps to get it running.

You can also contribute your own reports to ProtonDB! If you decide to try out a game with an unknown rating and find that it works, submit a report and let others know!

Desktop Mode

Speaking of other games or emulation, should you decide that the default SteamOS experience in Game Mode is too limiting, you can easily flip over into Desktop Mode, in which case you're now interfacing with the system as a full-fat Linux distribution. Most people won't ever need to do this, but the option is there if you want it. This is where you can do things like set up emulation, install Diablo 4 or add games from stores like Epic or GOG.

You can still use the keyboard and mouse in Desktop mode, but it's a little clunky, so I got myself a small foldable bluetooth keyboard to use if I'm ever doing anything intensive there.

ProtonUp-Qt

If you do venture into tinker-land with Desktop Mode and want to try out potentially unsupported games, ProtonUp-Qt is a great tool to have. Proton is Valve's compatibility layer (like WINE) that lets the Steam Deck run Windows games. ProtonUp-Qt is a way of installing third-party versions of Proton, which sometimes allow different games to run. The main third-party Proton release of note is ProtonGE (or "Glorious Eggroll"). This is a version that has some extra fixes or things that Valve can't necessarily add to their version. If I can't get a game to work under the regular Proton, I usually try this one.

In general, if you go into a game's properties, you can change the version of Proton that it runs with. For most games you'll never need to do this, but if you can't get something working, you can use ProtonUp-Qt in Desktop Mode to install the latest ProtonGE, then go back to Game Mode and tell the game to launch using ProtonGE instead and try that out. It sounds a little complicated, but after one or two times it becomes second nature.

Also, Valve includes previous versions of Proton with Steam itself. Occasionally you might see a note on ProtonDB to roll back to a specific version of Proton in order to get a game to run. Go into the properties, select that one from the list, and you should be good to go.

There's a couple of things you could look into that may be particularly helpful.

Decky, which allows installing plugins, and the plugin is Powertools. This lets you more finely adjust how performant the device will be, and opens up some options that may help with specific games and emulators.

Emudeck is a comprehensive collection of emulators and configures itself to be pretty easy to use. It does a decent job explaining itself.

Cryoutilities is a little application made to help out performance by changing a few under the hood settings. It isn't going to be a night and day difference but for some games may make just enough of one.

Cryoutilities will also make you aware of something you can change with or without it. If you hold + while booting you'll enter the bios. In the setup utility there, you can change a setting called UMA frame buffer (or something similar to that) to a maximum of 4gb. This is helping to allocate video ram and changing this setting is telling it to allocate more. At least from the testing in cryo's videos, 4gb appears to help and outside some rare edge cases has few if any downsides.

The combination of all of these things sets you up for making the device perform as well as it can. With Decky you can also use VibrantDeck to make the screen look nicer, and Fantastic to set up a different fan curve. These aren't necessary and won't necessarily do anything for performance, but can make it look nicer and run a little less noisy. Letting the deck get a bit warm won't hurt it.

Besides those it's just down to checking out what all is in the settings on the device itself. Give those a once-over before you get to playing is all Id really say for that.

Allow me to apologize on all my Tildes friends here for missing a crucial part of this:

having never been a PC gamer.

Welcome to your new lord and saviour, steamDB.
https://steamdb.info/sales/history/
This is your absolute 100% pathfinder to the deep repository of games that Steam has, as well as your compass towards the very notion of STEAM SALES.

There are literally THOUSANDS of games that will go on sale Nov 21st (8 days from posting) for $2-5 that are absolute bangers. You have the universe's permission to just bury yourself in a steam-backlog that will take you decades to burn though on your deck.

Emudeck is pretty easy to setup and opens up a wide range of emulation options for the Steam Deck. That has been the biggest personal game changer as far as capabilities of the Steam Deck.

The biggest tip is IIRC you still need to change a setting to be able to download and play unsupported games.

In settings you need to change "Enable Steam Play for supported titles" to "Enable Steam Play for all titles"

I know it's not quite the scope of the question but Dead Rising runs amazingly well on the deck.

Learn to use the back buttons and limit the screen refresh rate to 40hz...

Unless you're playing something like Brotato, which has a ton of stutter under 60hz, so basically get comfortable tinkering a bit but also the Steam Deck is a great machine out of the box so don't feel required to go on YouTube and install dozens of tweaks - just get started gaming and if it feels off then make changes.

Pretty simple but: you can hook up a mouse and keyboard (I use Bluetooth) and a PC monitor, and they will work in SteamOS mode and desktop mode. If you're planning to do significant amounts of work messing around with software/settings in desktop mode, especially in the terminal, I would highly recommend you set up at least the mouse and keyboard. Your thumbs will thank you later.

• Burnout Paradise (not remastered) runs great on the Steam Deck, the servers have been shutdown so you have to skip logging in every time but it's still a fun racing game.
• Stardew Valley runs great but inventory related stuff is slower compared to using a mouse.
• Backpack Heroes
• Dicey Dungeons
• Cassette Beasts - I had issues with the game's design but it runs great
• Cat Quest - Runs great plays great
• Cat Quest 2 - Runs great but not as good as CQ1, difficulty is inconsistent
• Cave Crawler - Free to play so why not?
• Dwarf Journey - A fairly simple action platformer roguelike
• Enter the Gungeon - Bullet hell shooter
• Holocure - Free to play reverse bullet hell shooter, play if you watch any of the Hololive VTubers
• Mr. Shifty
• Patrick's Parabox
• Peglin
• Potion Craft
• Rain On Your Parade
• Rimworld (I've only played this on desktop)
• Roots of Pacha - Neolithic Stardew Valley but not as good
• Sable - Feels more like a tech demo than a game, has a truly unique art style
• Shadedown Hawaii
• Slay The Spire - Well regarded but my brain is too smooth for me to be tactical
• Streets of Rogue
• Terraria - I didn't like the controls but maybe you'll fare better

Pokemon Infinite fusion runs great but is a bit of a fiddle to install on the Steam Deck

I love The Binding of Isaac series and it's great on Deck bc, as others have mentioned, low resource games give you more time to game.

Darkest Dungeon is another one I enjoy - touchscreen FTW here.

Vampire Survivors and Halls of Torment are great, too.

Dead Cells and Sundered are good candidates, if you like roguelike metroidvanias.

I've been replaying Cyberpunk 2077 on my Deck and I'm pleasantly surprised how much I enjoy the experience, although I don't get much playtime if I'm not plugged in.

ETA - Brotato is fun af, easy on battery, AND on sale on Steam right now.

As someone else mentioned, use the Heroic launcher to get your Epic games. You can have it make steam shortcuts for you so that you can easily find your games in gaming mode. One issue I encountered is sometimes Heroic would get logged out of Epic and games wouldn't launch, with an error saying the game wasn't installed or something. I think this is because I signed into Epic on too many devices. I now only stay logged in to Epic in Heroic and in my phone's browser to get the free games.

From those games I can highly recommend Celeste (platformer - personally I'm not a big fan of the story but the gameplay is great) and SUPERHOT (FPS, haven't played this one on deck yet but I loved it when I played on PC), Bioshock (FPS/RPG, also haven't played on deck, just on Xbox 360).

For Steam games, there are a ton...My top picks for the deck would be Halo: Master Chief Collection (FPS) and Slay the Spire (roguelike deckbuilder). If you are able to play multiplayer (either locally with a dock and some controllers, or over the internet with your friends) then Duck Game (2D platformer shooter?) is a blast.

Once you've gotten your non-Steam games added to your library, I'd recommend heading over to SteamGridDB to get those games looking spiffy in the library UI. They even provide a program, SGDBoop, that automatically adds the assets into Steam for you.

Elden Ring is shockingly good on the Steam Deck, it's the main game I've been playing on mine! I've also enjoyed Wargroove 2 and Hardspace Shipbreaker on it!

The fact that you are on PC means your back catalog stretches back through the whole 7th gen of game consoles and even some late 6th gen or earlier stuff is available on Steam.
Worth considering if you ever want to dust off something from the PS3/360 era.

Does the steam deck offer game streaming from desktops? I'd love to play cities 2 on the couch and stream it from my desktop.

How does it compare to the game streaming of the ally or legion go?

Little off topic, but where did you get your refurb @Evolone?

Shameless plug for the Steam Sales thread, feel free to ask questions about games you're interested in!

There's also a weekly thread called Save Point that aggregates deals, feel free to be inspired by that thread too

Disclaimer to never overspend on your steam library!