Petrov - modern attack - Symmetrical variation
1. e4 e5 2. Nf3 Nf6 3. d4 Nxe4
White pushes the king's pawn to e4. Black pushes the king's pawn to e5. White develops the knight to f3.
Black develops the knight to f6. White advances the queen's pawn to d4. Black captures with the knight on e4.