Against the Alapin: the anti-Sicilian you'll meet most

The key idea

Against 2.c3 Black hits the centre immediately with ...d5 or blocks it with ...Nf6, not letting White build d4 in comfort. And there's a detail that changes the game: by playing c3, White has taken that square away from his own b1 knight, which will take much longer to come into play.

Example 1 · ...d5 at once, and the queens come off

2...d5 strikes before the centre exists. White trades and Black recaptures with the queen without trouble.

1. Nf6 My queen is on d5 and that frightens a lot of people, because it looks like it'll be chased with tempo. Notice why it isn't: the natural square to hit it would be c3, and his own pawn is sitting there. By playing 2.c3, White has taken away from himself the move that would punish my queen.
2. dxc5 White resolves the tension and offers the queen trade. It's his way of getting a comfortable position without complications.
3. Qxd1+ Happy to trade. Without queens, a big centre is worth much less: there's no attack to be had, and all that's left is the structure — where I'm perfectly fine.
4. Kxd1 His king has to recapture and loses the right to castle.
5. Bg4 And I take advantage: I pin his f3 knight, which is what defends his c5 pawn and his centre. Every move of mine comes with a small threat, which is how you play when your opponent has lost castling.
6. Be2 White defends and prepares to connect his rooks.
7. O-O-O+ I castle long WITH CHECK, which is the detail that settles how comfortable this position is: I put my king safe and activate a rook in a single move, and he spends three moves placing his by hand.
8. Ke1 His king walks back to the centre. Balance: a level position and a far easier one for Black to play. Against the Alapin you don't need to know anything — you need to strike early and to know that his c3 pawn gets in his own knight's way.

Example 2 · ...Nf6 and the pawn that goes too far

2...Nf6 provokes 3.e5, and from then on that pawn is a target. The second way to answer, just as natural.

1. Nc6 The other answer: instead of striking with ...d5, I provoke. With 2...Nf6 I force him to push to e5, and that advanced pawn, which looks imposing, is above all a target — it's far from home and no pawn defends it.
2. cxd4 White recovers his pawn, as expected.
3. d6 And here's the thematic blow: I attack his e5 pawn from underneath. The usual rule against an advanced pawn — don't surround it, undermine it.
4. Bc4 White develops, hitting my central knight.
5. Nb6 My knight retreats gaining a tempo against his bishop. Notice I've lost nothing: he has moved the bishop once and I've moved the knight twice, but every move of mine came with a threat.
6. Bb5 The bishop moves again, this time to pin.
7. dxe5 And I capture the advanced pawn, which was the target from move 2. Without it, White is left short of space and without the edge he was after with the whole variation.
8. Nxe5 It gets traded and the position is level. Keep both roads together: against the Alapin you can strike immediately with ...d5 or provoke with ...Nf6 and undermine afterwards. Both are natural moves, neither requires memory, and both work because they attack the same thing — the centre White needs to build for his opening to make any sense.

Practice

Your queen is on d5 and can't be chased with tempo, because his own pawn occupies c3. Develop naturally, trade queens when he offers it, and activate your pieces.

1. Natural development. Your queen is comfortable on d5 precisely because his c3 pawn takes that square from his own knight. Bring the g8 knight to its natural square, defending your queen along the way.
2. Happy to trade: without queens his big centre is worth much less, and he loses castling. He's offering the queen trade. Take it, and with check.
3. You pin the defender of his centre. With your opponent unable to castle, every move of yours should carry a small threat. Bring the c8 bishop out to pin the knight defending his centre.
4. King safe and rook activated in a single move, and with check on top. He spends three moves placing his by hand. Castle on the long side. Check first that it also gives check.

Against the Alapin you don't need to study: you need to understand what White wants — a big centre with d4 supported by c3 — and not let him build it. Strike with ...d5 at once, or provoke with ...Nf6 and undermine the e5 pawn afterwards. And keep the detail that makes the whole line comfortable: by playing c3 he has taken that square from his own b1 knight, so his development is always a step behind yours.