recommendation?


YouTube is trash.4
Books are the way to go, but many don't know how to use them. Like in say, the Opening Repertoire or the Move by Move series from Everyman, one game should take you about 90 minutes. Many just rush through. Many try to memorize. Biggest mistake ever! You need to analyze and UNDERSTAND!

Find openings and understand the middlegame plans. If you like youtube, I would recommend checking out ChessGeek's Opening Masterclasses as they are fairly good and comes with a pgn. But as @ThrillerFan said, books are better because they are usually given by a master who knows the opening well and usually explains the content in great depth. Now, don't go straight to the Grandmaster Repertoire books as those (even for me) as they are meant for Masters.
What I like to do if there is no book on an opening I want to learn is go use a database and find model games and annotate them. They will suck at first but eventually, you will pick up on some ideas and by going through some variations yourself, you will start to understand different plans