The rook is a very powerful piece, especially if you know how to make the most of it. In this first example, the black rook is in the corner where it begins the game. To make the rook as good as possible, try to move it to an open file where the pawns can't block the rook from moving forward. Rooks are more powerful on open files because they can then control the middle and far reaches of the board.
If it's good to put one rook on an open file, it's even better to put both rooks on open files! From these squares, the rooks help to control the important center of the board.
In the final example, we have two rooks but only a single open file. We therefore start by moving one rook to the open file and then moving it forward to make room for the other rook to move behind it. This is called "doubling rooks."
