Thats good.
Ok so you have to go to "My Mibba" and scroll down until you see the "My stories" heading on the side. Click on the one that says My Stories (or something like that), click on the title of the story you have there, and then click on the little "Add chapter" button underneath. There might be an easier way, but that's what I do.
And I can never type out work. It always comes out as owkr xD