Before using these ideas the usual sacrifices may be needed to open the long diagonal for the bishop or queen, to create a safe square for the knight, or both. Here you should see that White has a bishop on the long diagonal and a knight on f5, with the knight ready in principle to support mate from e7 or h6 if the diagonal can be opened. Hone in on the impediment: the pawn on g7. The best way to clear a pawn is to take something it protects or to make a threat from a square it guards, forcing it to capture and leave its line. So White plays the mate threat Qh6. Black is forced to reply g7xQ to avoid Qxg7#; yet this opens the diagonal and allows White to mate with Nxh6 (not Ne7, since then Black has NxN). Qh6 is a classic technique for creating an open diagonal to permit a mate of this type.