The rook is lesson 1 of 6 in How the pieces move, a basics course suited to players rated around 150 (complete beginners). The rook moves in straight lines: up, down, left or right. It has 4 interactive exercises: 4 star-collecting exercises. You play every move on a board and get feedback straight away. The lesson is free.
What this lesson explains
The rook moves along files and ranks, as many squares as it likes. It cannot jump over other pieces.
What you practise
Move the rook to the star: drag it, or tap the rook and then the square.
Now the star is not in a straight line. A rook needs two moves for it.
Collect all three stars.
Your own pawn blocks the way. Find a path around it.