Ask what White attacks. There are three answers: his rook on g1 attacks the knight on g4; his bishop on d3 attacks the bishop on g6; and his queen on h3 attacks the pawn on h5. All three possibilities are useful and important. The first thing to see about them is that White has the makings of a pin on the h-file, as his queen bears down on Black's pawn and then also a piece behind it. This is of particular interest because the h5 pawn is all that guards the Black knight that your rook would otherwise be able to take. What prevents the pin from succeeding is the protection the rook takes from the Black king; White's threat to take the rook with his queen isn't scary so long as the rook is guarded. The challenge is clear: interrupt that protection. We know a few ways to do this. One is to distract the guard by taking something else it protects. In this case the king also guards the bishop on g6. So White plays 1. BxB, KxB; this leaves the rook loose and thus causes the pawn on h5 to be pinned. Now White can play RxN+. If Black recaptures with h5xR, White takes Black’s rook with his queen and still has won a piece.
As you can see, the idea of loosening a screened piece to create a pin of whatever lies in front of it has great practical importance. Whenever you see enemy men lined up in front of one of your attackers, consider whether loosening one of the rear ones—by any of the means we have considered here—would leave the one in the foreground pinned and useless as a defender.