How do you play janken (scissors, paper, stone)?

Janken is played to determine who wins and who loses.
It is usually played with one hand to make one of three signs at the call "jan-ken-pon": Gu (stone) is shown with the hand in a fist, par (paper) is shown with the hand open wide, and choki (scissors) is shown with the forefinger and middle finger open, or the thumb and forefinger open.
Gu wins over choki, choki wins over par, and pae wins over gu.
If the players show the same sign and can't decide who wins, they repeat the motion with the call aiko-de-sho, which means tie.