Building a bridge (Lucena)
The most important winning technique in rook endings: free your king from the checks by building a bridge with the rook.
The Lucena position
White's pawn is one step from queening, and the rook on the c-file keeps Black's king away. The trouble is White's own king: it blocks the pawn, and when it steps out, Black's rook checks it from behind. The solution is to bring the rook to the fourth rank, where it can later block those checks. This is called building a bridge.
Push the king away, then build
Your turn
First check Black's king one more file away. Then put your rook on the fourth rank.
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Rd1+ pushes the king to the e-file, and Rd4 builds the bridge. The rook waits on the fourth rank for the checks to come.
Walk out and block
Your turn
Walk your king out toward the rook, and when the checks run out of room, block with the rook.
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Rb4. The checks are over and the pawn queens. You have built the bridge.
Check yourself
Question
With the pawn on the seventh rank, which rank does the rook go to for the bridge?
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The fourth rank
From the fourth rank the rook can block a check on the b-file once the king has walked down to b5.
