The Advance and Steinitz lines create the classic French chain: White pawns on d4 and e5, Black pawns on e6 and d5. White's chain points at the kingside, so White attacks there. Black's chain points at the queenside, so Black attacks there with ...c5, ...Qb6 and sometimes ...b5-b4.
The guiding rule, set out by Aron Nimzowitsch, is to attack a pawn chain at its base. For Black that means d4, which is why ...c5 appears in almost every line. The secondary target is the head of the chain, e5, attacked with ...f6.
In the Winawer (3.Nc3 Bb4) Black often gives up the dark-squared bishop for the c3 knight. White gets doubled c-pawns and the bishop pair; Black gets a solid position and long-term targets on the queenside.