Help:User pages
Every registered user on Shifti gets his or her own "user page", a page with the same name as their user name located in the user namespace. A link to your user page and its associated talk page are present at the upper right corner of the default skin. Links to your user page will also be automatically present in your signature and in the editing history of pages you've worked on.
Your user page is your castle. It's intended to serve as a "home page" that you can format any way you like. You could use it to display a list of your own stories, a list of your favorite stories by other people, links to other sites, and so forth. Shifti has an extension called KeepYourHandsToYourself installed that automatically protects your user page against editing by anyone other than yourself (and administrators).
Your user talk page is not protected against editing since it's intended as a forum where other users can post notes for you to see. However, it is still considered "yours" and you are generally free to remove comments posted by other users if you like. Please do not edit the content of other users' comments, however. See Help:Talk pages for more details on the use of talk pages.
User subpages and posting stories to them
In addition to your root user page, you can also create pages that are "subpages" of your user page. Subpages are created by adding a forward slash after your user name and then putting the subpage's name after that. Subpages are protected against outside edits in the same manner that the root user page is. For example, the user pages User:Joe Bloggs and User:Joe Bloggs/Magic Cheese can only be edited by Joe Bloggs himself, but User talk:Joe Bloggs and User talk:Joe Bloggs/Magic Cheese are open to the public.
Subpages are commonly used for posting stories. Note that if you want other users to be able to edit your story, for example if you're requesting assistance in copyediting, you shouldn't put the story in a user subpage. There is no way to selectively allow user subpages to be publically editable.
Since having "User:Joe Bloggs/" in giant letters at the top of every story is often displeasing to the eye, the automatic page title header for user pages and subpages has been disabled on the default skin. If you're posting a story in your user space you'll probably want to add a title header yourself, possibly using the "title" template.
Formatting
User page format is up to the individual author, they can do whatever they like with them. However, there is one template available that can be useful to provide an easy and consistent way of linking to one's story category: {{my stories}}. See Template:my stories for documentation.