What's the best way to learn in this game?

I feel that I didn't learn much I started since legion, blight and now still as noob as ever and as usual I just copy the build I'm interested without paying much attention to what this skill gem do, didn't read much of detail guide. Where and how should I start learning the game

Playing the game for yourself, whithout following other's builds. Make a new char and play with your own build. Make mistakes. There's no better way to learn that die and try to understand your mistakes.

The game takes both study and practice to get good. You can do the study part through guides, videos, the Wiki, the forums... or all of those.

A good guide is useless if you don't study it to understand how all the parts work together. Your own failures are useless if you don't evaluate them to understand what happened.