Many users like to create user subpages to store various bits of information such as welcome templates or other information. For example, if you are drafting a new page that is not ready to "go live", or proposing major changes in redrafting an existing page, a user subpage may be very useful.
To create a subpage simply visit your User page and then append the name of the subpage in your browser's URL bar. For example, http://en.wikipedia.org/wiki/User:CoolDude would become http://en.wikipedia.org/wiki/User:CoolDude/MySubpageName. When you press the ↵ Enter key you will be prompted to create the new subpage.
If you no longer need a subpage, or wish to have it deleted, you can mark the page with {{db-owner}} or {{db|reason}}.