You can specify where users can create SharePoint sites. If you do not change the default settings, sites will be created ...

You can specify where users can create SharePoint sites. If you do not change the default settings, sites will be created in the same database as the portal site and will have the same prefix. If you want to specify the URL from which users create sites from the Site Directory, type the URL in the URL box. The URL must point to a Web server running Microsoft SharePoint Foundation, with Self-Service Site Creation enabled. If you do not type a URL in this box, users will create sites from the default site creation page for this portal.