Against a rook pawn on the sixth with the enemy rook in front of it, the defender attacks the pawn from the side along the sixth rank, keeps the king on g7/h7, and checks the attacking king whenever it approaches the pawn.
Vancura's position is the key to defending against a rook pawn on the sixth rank when the attacking rook stands in front of it. Black's rook on f6 attacks the pawn from the side, so the white rook is tied to its defence, and Black's king sits on g7 where it is safe from back-rank tricks.