Evans gambit declined
1. e4 e5 2. Nf3 Nc6 3. Bc4 Bc5 4. b4
White advances the king's pawn to e4. Black moves the king's pawn to e5. White develops the knight to f3.
Black develops the knight to c6. White develops the light-squared bishop to c4. Black develops the dark-squared bishop to c5.
White moves the b-pawn to b4.