The Lucena Position
Rook and pawn endings are very common and often surprisingly difficult. It is a good idea to build up knowledge the basic rook and pawn endgings so you know which are won and which are drawn, and how to play them accurately.
The Lucena position is one of the most important endings to learn. The side with the extra pawn can win with the right method.
This is a good position to practice with a friend!