How to learn an opening?


It's good to learn your opening(s) well, but you don't need to memorize variations you aren't planning to play. It's more important you understand the ideas behind the moves; that's true for any variations. You don't need to memorize things though; it isn't practical to brute force memorize everything. Chess has over one thousand chess variations and each variation has their own details to learn.
It's better to focus on concept like this: https://www.chess.com/blog/KeSetoKaiba/opening-principles-again


What I started doing recently is learn few most important variations and then find critical position and explore few games from that position. Then I just take that position and draw arrows with typical ideas. Like this:
How does one find the 'best' opening befitting to the 'style of play'? My opening theory ends on move 3-4...
Nf3 - c4 - e3/b4/b3/Nc3/g3 for white,
d4 d5 - c4 c6 - Nf3 exc4 for black,
or d4 Nf3 - c4 e6 and hope for Nf3 to play c5+b5
e4 e5 and hope not to get anything besides Italian,

I think the best teacher is practice and consistency.
Once you practice an opening over and over, it will come as second nature to you to understand the best move in each position.

Good idea also. It sometimes discovers principal things - that the opening has totally different concepts and ideas.

Hi @Milch_Tee
You don't need to learn ALL the variations, most strong players don't even know this. It's much more important to understand the IDEAS of the opening. What are you aiming to achieve? Because eventually both players forget the theory, but the person who understands the position better usually comes out on top.
To understand the IDEAS, I genuinely think watching the 10 min YouTube summary's of your opening are helpful because people will talk about these ideas frequently. Then it's a matter of playing it many, many times and seeing these ideas for yourself
Hope that helps,
@FinkeChess