Center Game Accepted is a chess opening with the ECO code C21. It goes 1. e4 e5 2. d4 exd4. White opens with 1. e4 (the king's pawn) and Black answers 1... e5. After 4 moves it is White to move. After the last move Black is a pawn ahead in material. 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 3. c3, 3. Qxd4.
After 1.e4 e5, White plays 2.d4 at once. After 2...exd4 3.Qxd4, the queen comes out early and can be chased.