Figure[White to move]

Here the initial idea is easy enough to see but its consequences are a bit more complicated. Black’s king is trapped behind its pawns and White has a battery of rooks directed at d8, clues that should get you looking for a back rank mate. Black guards d8 twice, with both of his rooks, so pounding away at that square doesn’t work by itself. But White has another resource he can use to remove one of Black’s guards: 1. QxR. Now White threatens to mate with 2. QxRe8. If Black replies to QxRa8 by recapturing RxQ, then of course White has 2. Re8+, RxR; 3. RxR#. Black can avoid this fate, but only at great cost:

(a) If Black replies to QxR by advancing his h-pawn to give his king breathing room, White has QxR and now has taken both Black rooks. A brutal attack then follows as White closes in on Black's king with his queen and both of his rooks. White has an eventual forced mate.

(b) Black can instead reply to White’s initial QxR by playing Kf8, permitting his king to protect his rook. But White already has won the other rook, and now he can press a powerful attack by playing Rd8, creating another mate threat (RxR#). Black plays f7-f5, opening a line of protection from his queen to his rook; but now White can perform the exchange RxR+, QxR—and then White brings his other rook to d8, pinning Black’s queen and winning it (Black plays QxR; White plays QxQ+).