Ruy Lopez - Caro variation
1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 b5
White pushes 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 b5. Black advances the a-pawn to a6.
White deploys the light-squared bishop to a4. Black moves the b-pawn to b5.