You are supposed to pass though many obstacles and enemies. once you hit enemies with your head you kill them. However, if they or the obstacles hit part of your body you will lose that part. also, that part will be petrified in the space and will be another obstacle to you future lifes. the longer distance you have achieved, the better player you are.
In the folder release, you can run the game double clicking on the ggj2012-medusa-runnable.jar file or using the run.sh and run.bat.