Repetition is key here. And solving problems.
I started many years ago with a "for beginners" book, and didn't fully understand a lot of it by the end.
So I started trying to build something, and searched for answers to the things I couldn't figure out (and went back to the book numerous times). I don't think I ever finished that project, but by persisting through it, and figuring out how to solve the problems that I ran into, I learned how to build something, and it stuck.