1...Nf6 move order and ...c4 is variation 5 of 5 in the Stonewall Attack course, a beginner opening course for White (ECO A45). It runs 23 moves and begins 1. d4 Nf6 2. e3 e6 3. Bd3 c5 4. c3 d5 …. Black starts with 1...Nf6 and plays the d-pawn later. Then Black closes the queenside with ...c4. White keeps the bishop on the h7 diagonal and attacks on the kingside. In the lesson every move is explained on a board and then drilled; it is free.
Move by move
1. d4 – White takes the centre.
1... Nf6 – Black starts with the knight and keeps the d-pawn flexible.
2. e3 – The calm Stonewall move.
2... e6 – Black opens the way for the dark bishop.
3. Bd3 – The bishop aims at h7.
3... c5 – Black hits d4 before playing the d-pawn.
4. c3 – White holds d4.
4... d5 – Black finally puts a pawn on d5.
5. f4 – Now the stone wall stands. The pawns on c3, d4, e3 and f4 are in place.
5... c4 – Black closes the queenside and attacks the d3 bishop.
6. Bc2 – The bishop steps back but still aims at h7.
6... Nc6 – Black develops the knight.
7. Nf3 – The knight heads for e5.
7... Bd6 – Black's bishop looks at f4.
8. O-O – White castles.
8... O-O – Black castles too.
The lesson goes on for 7 more moves, each with its explanation.
chessGM