Can someone explain what it means to study a chess opening?

I'll try.  There is a certain amount of memorization necessary.  The difference between the Italian and the Ruy Lopez for instance is where white's light squared bishop goes; c4 is an Italian, and b5 is the Ruy Lopez.  You have to start with that.  Now beyond that are a number of logical lines that you may well be able to figure out over the board, but have been played so often that they have become part of theory for that opening.  Researching the history of an opening can help you understand the "why" behind the moves and how evaluation changed over the years.

Why not just get a copy of van der Sterren's Fundamental Chess openings (FCO) and read about a few openings to see what I mean.  Oh, by read, I really mean study with a chess set unless you are an absolute genius who can keep it all in your head...

Thank you so much!

This is very helpful

Also studying an opening depends on what your rating is.  Below 1000 it makes no sense to study lines any deeper than 6 or 8 moves.  Your opponents usually won't have a clue what you are doing and you will usually be out of book well before then.  An 1800 may well know certain lines of his preferred opening over a dozen lines deep.  A titled player who likes the Najdorf may need to know 20 moves deep.  These aren't just memorized though;  you need to know the reason for each of these moves so that if your opponent deviates from theory you can punish them.  For most of us, just knowing opening principles is enough and then you can wing it from there.  Of course most of us have no ambitions to do more than have some fun killing a few hours playing chess.  If it becomes more than that; well,  there's a lot of studying to eventually do.  Good luck whatever level you are aiming for.

Just to add onto baddogno response, its helpfull to know your move orders, in the caro can, i play bf5 in the advance variation, the key pawn break is c5. If they give a check i play nd7 etc, but the idea is that white wants to cramp blacks position, black wants to prove whites over extended and undermind the center pawns. But theres are 500- 1600 lines in an opening. Memorizing the main ones in important just to get me into the middle game with a solid position. Beyond that all the other variations i go over is just to give me an stategical idea, I also know what my opponents best moves are and what the sidelines are. But people at my rating level dont play theory on move 10-15 unless its stockfish which happens. A good place to study openings is chessable, but puzzles, basic tactics, endgames should come first.

Start with tactics, you had free queen in your last game, the rook was pinned to the king.