The Sicilian is the fighting answer to 1.e4: instead of mirroring White you trade your c-pawn for White's d-pawn, keep both center pawns, and accept a sharper game in exchange for real winning chances with Black. It is the highest-scoring defense to 1.e4 at every level for a reason.
This lesson gives you the Najdorf move order with the classical ...e5 plan, the version where the ideas are clearest: a6 takes away the b5 square from White's pieces, ...e5 stakes the center, and the backward d6 pawn you're left with is far harder to attack than it looks. Deep theory exists here, but you don't need it yet; you need the skeleton, and this is it.
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Move 1 of 14
e4
White opens classically, and you are about to unbalance the game on move one.
Common deviations