Frustratingly (and in keeping with how confusing the messaging has been from the Australian government on all aspects of this pandemic), there is no single easy source that lists these new restrictions in a nice simple format.
All gatherings, whether indoors or outdoors, are limited to 2 people. Exceptions apply for people you're living with (you're already sharing germs with them). However, previous limits of 5 people for weddings and 10 people for funerals still apply.
People should only leave the house for necessary activities, such as: shopping for supplies, exercising, medical care, work, school.
Elderly people should stay home and self-isolate. This applies to: healthy people over 70; unhealthy people over 60; indigenous people over 50. (And if we ever needed evidence that indigenous people have worse health than everyone else, this announcement proves it.)
Public playgrounds, outside gyms, and skate parks will close.
These rules are all advisory, rather than legal. However, individual states can choose to enforce them legally.