The Lucena position

The Lucena position is a winning rook ending. You have a pawn on the seventh rank, your king is in front of it, the enemy king is cut off, and the enemy rook checks from the side. The winning method is called building a bridge.

1. Your king steps out from in front of the pawn, toward the side the enemy rook is not on, so the pawn is ready to move later.
2. Your rook leaves the pawn's file and interposes on the fourth or fifth rank, putting itself between the enemy rook's checks and your king. That block is the bridge.
3. Once the checks stop, your king shelters behind the rook and the pawn promotes.
4. The line below is only the start of that king walk: the black rook checks from the side and the white king steps between the pawn and the checks. It does not finish the bridge. Rook endgame puzzles are the practice set.

On the board