King's Gambit Accepted is a chess opening with the ECO code C33. It goes 1. e4 e5 2. f4 exf4. 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. Nf3, 3. Bc4.
After 1.e4 e5 2.f4, Black takes the pawn with 2...exf4. The game turns wild: White wants a big centre and an attack on f7.
chessGM has a full course for this line: open the King's Gambit Accepted course lesson.