How Do I Make A Database?

Hello everyone!

I've recently got an idea for a Database as a Service I'd like to create. The only issue is - I don't know how to create or host a database!

I've only ever used Mongoose/mLab with Javascript, and a minimal amount of Postgres with Python.

If I'm looking to create a database that will, eventually, be able to store images, songs, and videos, where should I start my homework?

I can create the backend and the frontend with no issue - just stuck on this part here. If it's of any relevance, I most frequently use the MERN stack.