Overview
With 2.c4, White threatens to exchange a wing pawn (the c-pawn) for a center pawn (Black's d-pawn) and dominate the center with e2–e4. This is not a true gambit, as Black cannot hold the pawn, for example: 1.d4 d5 2.c4 dxc4 3.e3 b5? (Black tries to guard his pawn but should pursue development with 3...e5!) 4.a4 c6? 5.axb5 cxb5?? 6.Qf3! winning a piece.
The Queen's Gambit is divided into two major categories based on Black's response: The Queen's Gambit Accepted (QGA) and the Queen's Gambit Declined (QGD). In the QGA, Black plays 2...dxc4, temporarily giving up the center to obtain freer development. In the QGD, Black usually plays to hold d5. Frequently Black will be cramped, but Black aims to exchange pieces and use the pawn breaks at c5 and e5 to free his game.
Read more about this topic: Queen's Gambit