Rock breaks scissors. Scissors cut paper. Paper wraps rock.

Score as many points as you can until you have no more possible moves. Make room for new pieces by removing old ones. Squares are removed when you wrap a weaker piece between two stronger ones. Since scissors cut paper, having scissors, paper, and scissors all in a row or column together will cause the whole set to disappear. Similar for combinations of paper-rock-paper or rock-scissors-rock.