3...Bg4: the attack on the queen is variation 3 of 5 in the Stonewall Attack course, a beginner opening course for White (ECO D00). It runs 23 moves and begins 1. d4 d5 2. e3 Nf6 3. Bd3 Bg4 4. f3 Bh5 …. Black's bishop attacks the queen on d1. White blocks with the f-pawn and hunts the bishop with a knight. Then White still builds the stone wall, with two bishops. 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... d5 – Black meets it.
2. e3 – The Stonewall start.
2... Nf6 – Black develops.
3. Bd3 – The bishop aims at h7.
3... Bg4 – The bishop attacks White's queen on d1. The e2 square is empty, so the queen is really attacked.
4. f3 – White blocks the bishop with the f-pawn and attacks it.
4... Bh5 – The bishop steps back and keeps an eye on the kingside.
5. Ne2 – The knight goes to e2, not f3. From e2 it heads for f4 to hunt the bishop.
5... e6 – Black opens the way for the dark bishop.
6. Nf4 – The knight attacks the h5 bishop.
6... Bg6 – The bishop steps back to g6.
7. Nxg6 – White takes the bishop. Now White has two bishops, and Black has only one.
7... hxg6 – Black takes back and opens the h-file for the rook.
8. f4 – Now the pawn goes to f4 after all. White has the stone wall and the two bishops.
8... c5 – Black hits the d4 pawn.
The lesson goes on for 7 more moves, each with its explanation.
chessGM