Ruy Lopez - exchange variation - 5.O-O
1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Bxc6 dxc6 5. O-O
White moves the king's pawn to e4. Black plays 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 captures with the light-squared bishop on c6. Black captures on c6 with the queen's pawn. White castles kingside.