Of course White can simply take a piece here with QxN+, and the temptation to play that move would be sore. But pause before playing even such obviously attractive moves to make sure you have nothing even better. In this case it's especially important because Black’s king is both exposed and constrained; this can lead to trouble for him in countless ways. The experiments begin by looking at checks you can give and finding Qf4+: safe checks you can give with your queen always need to be examined with care. This one forces Black to play his king to h5. Look for your next check. Follow-ups with your queen either lose the piece or are inconclusive, but don’t forget your pawns: White has g2-g4+. Black’s pawn on f5 can’t very well be used to recapture, as it now is pinned to its queen, so Black’s king is forced back down to h4 (h6 is under attack). See the resulting pattern in your mind’s eye: the king ends up in the same position where it starts, but now White has a queen on f4 and a pawn on g4—the kernel of a discovered check on the fourth rank. White simply steps the pawn forward to g5, forcing the reply Kh5 and winning the queen (g5xQ) next move.
The position is a final illustration of a valuable skill: the ability to see possible discoveries arise during the forced sequences you imagine. You think of a check, then your next one; but do you notice that one of your pieces has moved in front of another, making a new sort of threat possible? Consider this batch of studies—and this last one in particular—a way to build your instinct for that pattern.