The rook moves in straight lines: up, down, left or right, as many squares as it likes.
The rook cannot jump over other pieces. Because its own pawn is in the way, it can go up only as far as d5.
Move the rook to the a4 square.
If an enemy piece is in its path, the rook can capture it: it moves to that square and removes the enemy piece from the board. Capture the black pawn on d6.
The rook is a strong piece. It is worth about five pawns.