This mini-game helps understand how to play a rook against a bunch of pawns. The pawns are racing to promote and so the moves of the rook have to be precise.
The pieces move as in chess. Pawns go first. The pawns win if one safely reaches the other end i.e. is not immediately captured. The rook wins by capturing all the pawns. Experience confirms the principle that the rook should get (a) get onto the 7th rank and (b) get behind the pawns. There is no time to lose. Assuming Black plays well, the best move for White is 1.Rh7
The pawns must race ahead without delay.
White is just in time to catch the pawns.
Black is in zugzwang – any move loses.