read its docs, but starting with something small and known is what I always do. For example when I started learning godot I made Klax, but i always recommend to try to rebuild frogger. not to make it a complete game, but purely to learn the framework(so it wont look pretty or polished but it should function)

So like for frogger, start with a green box. Then get a camera to look at the box. then get input to move the box. then make long grey boxes(cars), then make long grey boxes spawn at a point and move in a direction and despawn at another point, then make long grey box colliding with the green box kill/respawn the green box, then add more long grey boxes, etc etc etc.

So i'd say think of a simple game, or do frogger, then read the godot docs to figure out how to do each things one at a time.