You are cute fluffy little bunnies 
and hop on the other bunnies' heads.

At the beginning you are in the menu, where you have to jump
over the tree trunk if you want to play and walk right.
Then you'll enter the arena. The aim is to jump on the
other bunnies' heads...

a,w,d to steer Dott
arrows to steer Jiffy
j,i,l to steer Fizz
4,8,6 to steer Mijji (on the numeric pad)

You can find more levels at http://www.jumpbump.mine.nu/cgi-bin/jb.sh
which you can start with: jumpnbump -dat levelname.dat

There are 15 additional levels in the data directory, load them with
jumpnbump -dat data/levelname.dat

there's a screensaver mode as well:
jumpnbump -fireworks -fullscreen

Network playing is untsted on the Amiga version.
Don't use F10 to switch to fullscreen, instead use 
-fullscreen from the command line.

Run with -h for more options.