4. Bc4 gambits a second pawn. It develops the light-squared bishop to a place attacking Black's weakest square f7.

Black almost always accepts the second pawn with 4...cxb2, rather than offering a transposition to the Göring Gambit with 4...Nc6.

In one rare line, Black advances the pawn to c2, not wanting to let White develop the dark squared bishop onto the long diagonal.

1. e4 e5 2. d4 exd4 3. c3 dxc3 4. Bc4

Wikipedia has related information at Danish Gambit.