If we have a rook against a pawn, what matters is the position of the kings, the rook and the pawn.
The goal of the stronger player ( the one having a rook ) is to cut the opponent’s king horizontally or vertically, so the king to cannot help to the pawn.
The next step is to move the king near to the pawn (to move the king into the so-called ‘square of the pawn’ ) and to capture it.
The next that must be done is a Mate with Rook and King vs. King.
