You’re experiencing the same thing everybody does when they start learning.
There are various things that I’ve NEVER seen explained properly, but you end up picking a lot up eventually by osmosis 
There’s a lot of rubbish tutorials on youtube, when they just immediately start coding things in the player controller, or game mode, without saying WHY they are actually doing this. And it often turns out to be wrong 
Best thing is to just keep going, and keep looking at different vids, and you will find your own way in the end.
There is no golden path to follow, I’m afraid. If only there was a big book…