If you are going to learn one sacrificial theme, this is the one.
Gunnar Gundersen White
A.H. Faul Black
Melbourne 1928
French Defense, Advance Variation C02
1 e4 e6 2 d4 d5 3 e5 c5 4 c3 cxd4?! 5 cxd4 ♗b4+ 6 ♘c3 ♘c6 7 ♘f3 ♘ge7 8 ♗d3
Beginners are afraid of doubled pawns after 8...♘f5 9 ♗xf5 exf5. Actually, they are not weak. The trade is balanced by the removal of White’s good bishop.
8...0-0?
9 ♗xh7+!
The basic ingredients of this theme are a castled Black king and the bishop sacrifice on h7 followed by a queen + knight trying to mate around h7.
Declining the bishop, 9...♔h8 10 ♘g5 g6, loses to 11 ♕f3 followed by 12 ♕f6 mate or 12 ♕h3.
9...♔xh7 10 ♘g5+ ♔g6!
The best practical choice. The queen drops after 10...♔h6 11 ♘xe6+.
He also loses too much material to stop mate after 10...♔g8 11 ♕h5. The key line runs 11...♖e8 12 ♕h7+ ♔f8 13 ♕h8+ ♘g8 14 ♘h7+ ♔e7 15 ♗g5+.
11 h4!
Once familiar with the sacrifice, you will find it easier to spot when ♗xh7+ is possible. But the proper follow-up can be harder:
White can let him escape with 11 ♕g4?! f5!. For example 12 ♕g3 f4! 13 ♗xf4 ♘f5. Or 12 exf6? ♔xf6 13 ♘h7+ ♔f7 14 ♘xf8 ♔xf8.
Question 21: Was there was another winning White 11th move?
11...♘xd4
Or 11...♕b6 12 h5+ ♔h6 13 ♘xe6+. Also 12 ♕d3+ ♘f5 13 g4.
12 ♕g4 f5 13 h5+ ♔h6 14 ♘xe6+ g5 15 hxg6 mate!
This is the oldest known sacrificial theme because of:
Gioachino Greco White
NN Black
1620
1 e4 e6 2 d4 ♘f6 3 ♗d3 ♘c6 4 ♘f3 ♗e7 5 h4 0-0? 6 e5 ♘d5 7 ♗xh7+! ♔xh7 8 ♘g5+ ♗xg5 9 hxg5+ ♔g8 10 ♕h5 f5 11 g6 ♖e8 12 ♕h8 mate.