Yeah memorizing lines is apart of learning the opening. I like to go through maybe 4 or 5 of the most common lines in an opening that I'm learning and review lines. Once you play more games you can add more layers to it and know what works when they play a move you haven't seen before.
How to learn openings?
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No, memorizing lines is the worst possible way of studying the opening.
Let me explain that first and then go on to give you some advice about studying openings. Learning lines out of your head does nothing to help you understand the position. It is a very common occurrence with lower rated players that they see their opponent making a move they have never seen before, and then not knowing what to do. These players will just try and follow the line that they've learned, which might not even make sense seeing the moves their opponent has played. 2 examples of this to make this obvious: if your opponent castles queenside instead of kingside, you can't go for a mating attack on the kingside, even though that always happens in the lines you memorized. Secondly, if you've studied the London, you're playing bad chess if you continue with your London setup after 1. d4 b6, because you can just grab the center with 2. e4.
Some advice about studying the opening. First off: don't. Don't study opening lines. It's not beneficial at your level. It's not needed up to a very high rating. I've seen players get to 2300 without studying opening lines. You're much better off studying tactics and middlegame strategy, so that you can win the pieces your opponents give away and can make normal moves when there are no tactics around. Not making mistakes is the way to get stronger.
For your opening moves you should then rely on the opening principles. These are:
1. Get control over the center (white wants e4 and d4 pawn center, black wants to prevent white from getting the e4 and d4 center)
2. Develop your pieces (move every piece only once and develop towards the center)
3. Get your king safe (castle)
Using the opening principles will mean that you're playing chess by learning ideas. This will help you play normal moves even when your opponent does not. If you adhere to these principles strictly, your openings will already be better than 99% of other people.
Sometimes you hear lower-rated players say that you can't play openings based on opening principles alone and that they need to study the opening too. This is wrong. The beautiful side-effect of playing the opening based on opening principles is that you're very likely playing the theoretical best moves anyway. Grandmasters generally don't do anything special the first few moves. The moves some other players might struggle to memorize are all based on these opening principles. Real opening theory only starts after a good amount of normal developing moves are done. Let me give you one example:
1. d4 (getting a pawn in the center)
1. ... d5 (preventing white from getting d4 and e4)
2. c4 (if black takes, white can play e4 and get the e4-d4 center)
2. ... c6 (if white takes on d5, we can take back with a pawn, so white can't get the e4-d4 center)
3. Nf3 (developing towards the center)
3. ... Nf6 (developing towards the center)
4. Nc3 (developing towards the center)
4. ... e6 (getting ready to develop Bf8 so we can castle)
5. e3 (same idea for white)
5. ... Bd6 (developing towards the center)
6. Bd3 (developing towards the center)
6. ... 0-0 (getting the king safe)
7. 0-0 (getting the king safe)
7. ... Nbd7 (developing towards the center. Pawn c6 is sadly in the way of the more active square, so black puts it on d7).
8. Re1 (developing towards the center. The real question at this point is what to do with Bc1: we don't want to put it on d2, cause it's not active. If we can get the e3-pawn out of the way, it can go to a more active square.)
8. ... b6 (Bc8 can only be developed to b7 with the knight on d7)
9. e4 (getting ready to develop Bc1 to an active square).
etc.
We just went over 9 moves of a possible Slav opening. No memorization needed, it's just opening principles. We can do this for many different openings with the same result.
The one thing this might leave you susceptible to is tactical tricks in the opening. It might be worth it to look for tactical traps in the opening you decide to play. You can also choose to let them happen and accept a few losses. After you've seen them once, you'll know next time to watch out for it. You could also look at typical traps in a certain opening. These traps are more often found in 1. e4 e5 openings. Because there are less traps in 1. d4 and because the middlegames are easier to understand, I've always taught my pupils to play 1. d4 when we started training together. As black we can just choose another move than 1. ... e5.
So my first advice is to not study the openings and to rely on opening principles instead. You can of course still reject this idea and continue to want to study the opening. If you do, please don't learn lines. Like I said before, that's the worst way of studying openings. If you must study the opening, go over games. Preferably annotated games with commentary explaining the moves. Every move is played with an idea and it's much better to learn those ideas. Maybe look for some other games too, where one player is a strong player and the other one significantly weaker. Like a 2400 versus a 1600 player. This will also teach you ideas and will teach you what you can do with the opening when your opponent makes mistakes. Usually the ideas in such a lopsided game are much more clear than in games between players of equal strength. Why I'm advising against this is because you're unlikely to understand the ideas behind all of the moves, even when it gets explained to you. You might 'see' that white has a space advantage, but think it's because of white's pieces instead of white's pawns. And even if you understand that white does have a space advantage, you will not yet know what to do with it and that it means that white doesn't want to trade pieces. This is because you don't know enough about the middlegame yet. And that problem is real, cause even if you're playing with a space advantage and then trading all of your pieces off, you're likely losing most of your games, because it was the wrong thing turning your space advantage into weaknesses.
When I was young and a much weaker player I've been there and done all of that. Reading through books not understanding the moves. Learning lines by heart. It doesn't work, it doesn't make you a stronger player. In fact, I got much stronger at a time where I avoided playing opening theory at all and I haven't studied opening theory since breaking through the 2000 barrier. You might even learn something you'll later have to unlearn because it was bad. Stick to opening principles and use the time to study tactics and middelgame strategy.
Do not learn, just play.
try to learn it by studying the moves lines and then practicing it in your games
How to learn openings? Do you need to memorize the bids?