To repeat: we arrived at this position by 1. Bxg6, Nf6; 2. Bh7+, Kg7; 3. Qg4+. It's Black's turn to move. He will lose his queen soon; can you see why? It’s because White’s queen will be able to check her way to f6 and threaten mate there, requiring Black to sacrifice his queen to get rid of the bishop on e5. But we're getting a little ahead of ourselves. From the diagrammed position Black has to play either KxB or Kh6 (if he plays Kh8, White mates with Qg8; notice that the f6 knight would be pinned). Black’s most favorable line is 3. …Kh6; 4. Qf4+ (working with checks to control the situation), KxB (if Black starts with KxB he ends up here a move sooner); 5. Qf5+, Kg8; 6. QxN, threatening mate, and now 6. …QxB to prevent it; 7. QxQ follows, and White has a won game.