Queen's Gambit Declined - 6.Nf3
1. d4 d5 2. c4 e6 3. Nc3 Nf6 4. Bg5 Be7 5. e3 O-O 6. Nf3
White plays the queen's pawn to d4. Black plays the queen's pawn to d5. White pushes the c-pawn to c4.
Black pushes the king's pawn to e6. White develops the knight to c3. Black develops the knight to f6.
White develops the dark-squared bishop to g5. Black develops the dark-squared bishop to e7. White plays the king's pawn to e3.
Black castles kingside. White jumps the knight to f3.