The rooks, which are also sometimes known as 'castles', are the second most powerful piece after the queen. Like the bishop they are long range pieces, but they do not share the bishop's weakness and can reach every square on the board. Because they start in the corners, rooks often don't join in the battle until after the knights and bishops, but that also means they often survive much deeper into the game. In fact, the most commonly occurring endgames in chess are endgames involving rooks! Each player starts the game with two rooks.
The rook can move any number of squares in a straight line horizontally or vertically, so long as none of the squares it passes through are occupied. The board below shows the legal moves for a rook:
Like the bishop, the rook can be blocked if other pieces get in its way. On the board below, make a legal move with the black rook:
Rooks capture the same way they move. On the board below, drag the white rook to make a capture:
That's not quite all there is to know about rooks - there is a special move called castling which involves a king and a rook, but that will have a page to itself later on.