Rook endgames are the most common endgames. Golden rule: the rook belongs behind the passed pawn. As the pawn advances, the rook's range grows.
Second rule: cut the enemy king off from the pawn. If your rook holds a file or rank and stops the king approaching the pawn, your own king can escort the pawn easily.
Third rule: keep your rook active. A passive rook that only defends usually loses.