How to study the Najdorf Sicilian? Help!

I think a combination is ideal. You want to know the more common variations more deeply, and the less common variations not as deeply. I also think it helps to do multiple passes, kind of like a parser does.

So when you're first developing your repertoire you might intentionally limit yourself to depth ~5-7 depending on the lines commonality. Just to ensure you get the basic overview, and settle on a coherent repertoire you're happy with. And from moves 1-3 maybe you cover every line played at least 1% of the time (with varying depths of course). But for moves 4-6... maybe you don't cover moves that are played <= 3-5% of the time, with some exceptions. And for move 7... maybe you move this to <=5-10%. etc..

You can adjust these numbers however you see fit, but the point is you have some limit both on how deep and how broad you go, and it differs based on the lines probabilities of being played.

Now on your 2nd pass... which you don't do until you're very sure about the 1st pass - so you know exactly which repertoire you want to play and why... you just modify those numbers. So now you go to depth 10-12... And now you cover moves <=3-5% starting at move 4, and <=5-10% starting at move 7, and then <=10-15% starting at move 9. etc. and maybe you adjust these numbers depending on the line you're in as well.

Of course your repertoire will continue to evolve as you play it and change your mind or experiment, so this is not a rigid process... think of it more like growing a plant, but at least there is some structure to it. But you don't want it to go too deep too fast or you'll prevent yourself from being able to experiment or change your mind. But eventually you'll probably settle on lines you like. So I suppose you're prioritizing breadth in a way, at least at first.

It's hard to give perfect advice in the abstract though. Because, for example, as black I ignored everything except for my response to 1. e4 and 1. d4 for a long time, just due to the sheer size of the repertoire otherwise. Until eventually I added some lines vs. the english and reti, but I still only know the first 5-7 moves of those. Though bear in mind - the e4 / d4 lines you play influence how you deal with the english / reti.

On another note... I don't recommend the Najdorf at your level. It's so theoretical and a6 is a more passive move, meaning there's too much theory and when your opponent goes wrong during the opening... you don't really get to punish him hard the way you do in other sicilians, like the classical where... for example, white can't even play the english attack setup or you have an advantage immediately.

I guess the first step would be to ask you if you know why all the above moves are played.

First get yourself a middlegame book on the Open Sicilian like Polugaevsky's Sicilian Labyrinth. If you don't have that background, if you have no grasp of what the Open Sicilian is about, opening moves are of no use.

Second you have to decide if you will play the variations with e5 or the variations with e6 (6. f4, 6. Be2, 6. Be3/6. f3, 6. h3 and a few others give you the choice, 6. Bg5 and 6. Bc4 not so much). e5 looks weird at first so you have to get familiar with the ways to handle this pawn structure. e6 looks more natural but Black is a bit cramped, so again it's not natural.

Third, you have to know 6. Bg5, 6. Bc4 and 6. Be3/f3 as deep as you can because it is a question of survival.

Then you have to know a concrete recipe for 6. f4, 6. h3, 6. Be2 and 6. g3, less in depth but you have to know some typical manoeuvers. The first two are trickier to handle so they need special care. 6. Be2 is usually very slow but very thematic, this is a good field to gain general knowledge about the Najdorf.

Then you need to take a glance at the other moves and decide which setup is best. Eg : there are many ways to play against 6. Rg1 but it's not as easy as it looks to keep the balance if White knows what he is doing.

I would say it's better to know the three main variations twenty moves deep, noting different offshoots of them and having some brief knowledge of them.

Something you have to understand about chess openings especially at the lower levels is that many of them are more "agreements" of how to play than actually attempting to maximize their winning chances. It's good to learn openings as a part of chess development, but it's not correct to think that 0.1 or 0.2 computer evalution improvement in moves is going to make much difference among lower rated players, especially online rapid or blitz. Once you realize that you are just agreeing to play into interesting lines or mainlines and that's why people end up learning 30 moves of theory - they're obviously not able to refute every single branch of moves that deep, even super gms tend to branch off before that, but sometimes it leads to a fun or interesting position they like.

I learned the Najdorf by playing it. And losing, a lot.

If you are afraid of losing, then chess is the wrong game for you.

After several years, I was able to play games like these ones:

Start shallow and wide. Deepen with time.

When I study an opening, I don't bother trying to learn theory 20 moves deep. I don't have the memory, the patience, or the time for that.

Though I do look through a database to identify variations that make sense to me, and ones that look fun/interesting to play.

Chess Tempo's free database (https://old.chesstempo.com/game-database.html) stops at move 10. If you click on individual games, you can see the whole game, of course ... but for the purpose of getting a "general idea" of the opening plans and ideas, I believe that 10 moves deep is certainly enough.

Especially if you're able to reach a point where you know that you can comfortably go 10 moves deep in any line or variation you come across in your games.

Also remember that you don't always need to play the main line or variation.

For example, against the Sozin (Fischer) variation with Bc4, the top moves after Bb3 are ...b5 or ...Nbd7.

But I don't like the potential tactics that White has at his disposal against the e6 pawn, with his d4 knight and b3 bishop both pointing at it, so I play a more conservative line with ...Bd7 and ...Nc6:

Certainly not cutting edge theory ... but it's logical to me, and the engine confirms that it's fine, so that's good enough to play on, for me.

I suppose my main point is: don't feel pressured into only creating a repertoire that's purely top theory. It's A-okay to create a simple, practical repertoire that is designed simply to get you to a reasonable middlegame ...

Then you just "play chess" from there on out.