To create or edit your user page, you must be logged in. Once you're logged in, look for a link for your user name at the upper right of the window.
You can also just create a wikicode link somewhere (like a sandbox page or your talk page) like this:
[[User:username]], save the changes, click on the link and start editing your user page.
To make a link to your talk page you would use this wikicode: