Adding your contribution is easy: after register or logging in with Facebook, you can browse existing stories, read the ones that sound interesting and add your personal evolution of the events. Every story is made of clouds which are something like very small chapters. You can add a new cloud after an existing one, so to write a continuation, or write an alternative to a certain cloud, so to propose an other development of the plot. The only cloud which can not have alternatives is the first cloud. If you have a cool idea for a new story you can also start a new story. Other users will come and add their contribution to your beginning.