(C) Copyright. All rights reserved. John V. R. Doktor. 1997.
You must choose either Stone, Scissors or Paper. So must the computer. The one who chooses the mightiest tool wins; Stone beats Scissors - Scissors beats Paper - Paper beats Stone
The rules are ofcoure much more complicated than this, and if you are interested you can contact John V. R. Doktor, who then will make sure you receive the official quackistic user-manuel. It will cost you £5.