How do i study chess theory?

I really love chess, and i wish to improve at it, i've been studying it harder than my final exams (just kidding) and one thing i can't really understand is how to study chess theory, im a high level beginner (1100 elo) and i want to get better understanding of my openings (Vienna and Caro-kann), i don't really think decorating lines is the best solution, but maybe understanding those lines may be best, but how do i do that? I don't know where to start that's the thing, watching YouTube tutorials may work but i mean, do they really explain much? What methods are there to learn chess theory? How do the top players learn it? Do i just get a book or something? Thank you for reading this, and don't worry, im not only focusing on my openings, i study my endgames too and i analyze my games.