You post a part of the story that is at least a tiny bit linked to the last part. You don't have to make up a character with a form or anything for it, Just add them in. Also, Write in story form. keep YOUR plot up, If someone interrupts it, Don't change it. Make a loophole for your plot to continue with the other persons plot still working. EXAMPLE
A Lady screamed in the distance. She was being tickled to death
The lady was yelling in pain but she wasn't being tickled anymore
just when the lady thought the tickling was over, It started again, and the assaulter started to use a feather.
I am epic
I am cool
I can't swim in a public pool
what am I?
And yes, I'm an Experienced RolePlayer
And Yes I like Minecraft
And No, I'm not a tomboy because I have TWO GAMES on my PC.
And Yes, I like trains.