How do I put up a short story?

Oh, I'm going to be a journal whore this week.

Ok, so I want to write a One-Shot, but I don't know how to set it as 'Short Story'.

Me and my stupidity will just end up putting it as a story with chapters and i'll only end up putting one up there and piss people off.

So I ask you, Fellow Mibba writers. To explain to me how to do this.

I really want to write a short story because I need to get my creativity flowing!
I don't want to post up another chapter for Draco's Diary until the contest is over.
And I'm writing most of my NaNoWrimo on my computer before I put it up on Mibba.

So yeah, I'm stuck.
In Short Story Purgatory.
Oh, Word! That Rhymed!

So... Help?