How to play the Old Benoni Defense

The Old Benoni starts with 1. d4 c5.

This pawn is not hanging due to Qa5+.

If they take, rather than Qa5+, e6 would be stronger. It attacks the pawn and they can't guard it with b4. Because after 3. b4 a5 4. c3 axb4 5. cxb4 Qf6 wins a piece.

White is lost here. If they don't defend and play something like Nf3, your bishop will take their pawn. They make a move and we play Nf6, followed by d5, castling and Nc3. We play Re8 and then e5 to better our bishop.

If they play the best engine moves, 3. Nd2 Bxc5 4. Ne4 Nf6 5. Nxc5 Qa4+ 6. Bd2 Qxc5, it goes exactly like that.

That was the "exchange variation," in a sense. It's not called that. The better move after c5 was d5. We will play e6, if they take we take back with the f-pawn. Usually it is bad to move the f-pawn, but in this case there is no immediate threat. We should play Nf6(unless they play e4) next and play standard chess.

We will prepare the d5 push. The better move was c4, defending their pawn. You will trade. You now play d6, your next moves will be g6 and Bg7. We do this because that diagonal is weak. If you know the King's Indian set up, that is what you will do kingside, by playing Nf6.

We have a weak e5 square as we only control it once. We will play Bg4 to trade off the bishop and then Nbd7 Ne5 creates a great outpost for your knight(later).

In the case above we should prepare it with something like Qe7, or Re8.