If you go to your mibba, on the right side there's bunches of orange menus, if you scroll all the way down to STORIES you'll see in it's menu 'stories', click on that and click 'add a new story'
Or, without scrolling down everywhere, on your about, you see your info about you and your avatar, and a link above you to Netapets, etc., right below 'info' you see 'quick links' next to the one that says "my stories"
you'll see one that says 'submit new story'