If you're
first starting out, then I think Chess.com's videos make a lot of sense so you know what getting into the Najdorf really involves. Once you've accepted how deep the rabbit hole goes, I would undoubtedly buy volumes 1 & 2 (at least) of
1.e4 vs The Sicilian by GM Parimarjan Negi in order to catch up on 6.Bg5-related theory.
In terms of what line's to look at... well, Negi has done a masterful work in taking apart the Najdorf (and the Classical Sicilian for that matter) with 6. Bg5. But, that doesn't mean there aren't holes in his analysis - already, you can find things popping up in GM play and on Chesspublishing.com too!
Speaking for myself, I've found a
potential vulnerability in the Polugaevsky variation of Negi's book - volume 1 - where Black neutralizes White's initiative with 22...Qd5 (which seemed pretty natural here. Here's a taster:
...Where I think a draw is the most likely outcome. I doubled checked w/ my computer (stockfish 8) and it puts it at 0.11.
To be honest, it strikes me that White won't know their theory here unless their in the IM/GM category. I really love the Polugaevsky variation and since the theory isn't super-well known (especially in Class A chess), I think Black has a massive OTB/practical advantage.
Best of luck on your journey.
~AP