King and Rook - Checkmate

In the king and rook endgame + V/S , you must keep the king and rook close to each other. If the kings are in opposition, when there is exactly one square between them, you move the rook up to attack the king. This forces the king backwards. On the edge, he can't move backwards, so it is checkmate. For more information, check the below position. 

In most cases, people would rather mate with the rook covering a rank, not a file, because it is more common. This is covered in the below example.

Hope you learned a lot! If you want to practice, visit this link :https://www.chess.com/drills/practice/rook-mate