Queen's Gambit is a chess opening with the ECO code D06. It goes 1. d4 d5 2. c4. White opens with 1. d4 (the queen's pawn) and Black answers 1... d5. After 3 moves it is Black to move. The lesson on the board explains every move of the line and lets you play it yourself; it is free.
In chessGM's opening book this position continues with 2... c6, 2... e6, 2... Nc6, 2... e5, 2... dxc4.
chessGM has a full course for this line: open the Queen's Gambit course lesson.