Okay. Covers. ^.^ Now, you gotta remember, I'm no expert. However, if you go and click 'create', that will take you to the page where all your stories are. Go to the working cover that you are automatically given when you upload a story. Beneath that, you can click 'edit'. On the pop-up, you can either select 'upload' and then upload your prepared jpg, which I think should be 256 X 400, but the pop-up will tell you. Or, if you click 'create', that will take you to a cover making program.
Or, if you're real lazy, like me, go to the cover making club and ask someone nicely to make one for you! Hahaha! There's probably more info in the help section too, in case you're interested. I hope that helped. :-)