Well this is simple. First, I'll start the story by entering a few words, like 'ROFL you just...' Then, someone else may for example continue it by saying: 'farted in...' Then, that may be continued by something else, and so on, and so on.
Rules: 1. Keep it as random as you can! 2. Be creative! 3. NEVER end the story! 4. Don't start a new story! 5. Keep your posts short and continuable! (is that even a word?) 6. If you wanna give a comment about anything, put it between ()!