The ladder mate (or lawnmower mate) is the first checkmate pattern worth mastering: two rooks, or a rook and a queen, take turns cutting off ranks until the enemy king runs out of board. One piece holds a rank so the king can't advance; the other checks on the next rank, driving it back; repeat.
It needs no support from your king and works from anywhere on the board, which is why it's the standard way to finish a game where you're massively ahead. Trade down, get your two heavy pieces out, and walk the enemy king to the edge rung by rung.
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The rook on g7 seals the 7th rank; the king is trapped on the edge. One rook climbs the final rung.
Finish the ladder.
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