You have a square 5 x 5 board with four rooks in the corners:
Note: for reference, assume the rooks are labeled A, B, C, D as follows:
A B
C D
You can move the rooks horizontally or vertically. The only problem is that when you move a rook, it will keep going in the same direction until it hits another rook or the edge of the board.
You want to move a rook into the darkened square on the board.