How do I actually learn Godot?

I mean to actually understand Godot. I have watched many tutorials, and they did help, but none of them helped me actually understand all the nodes and GD scripts so that I could have a base to start building things on. For example, if I search for GD tutorials for a 3D platformer, it surely will have some on YouTube, but if I finish that, all I learn is exactly what the tutorial shows, and I cannot create my custom mechanics beyond what the tutorial says. So that is the question again: how do I actually learn GD?