At the beginning you are in the menu, where you have to let each active player juimp over the tree trunk to enter the play area, and then walk to the right. You will then enter the arena. The aim is to jump on the other bunnies' heads...
Jump 'n Bump was originally a DOS game by Brainchild Design, which was open sourced under the GPL license and ported to SDL, and then SDL 2.