Adding a domain
First, open your app in vpsmodel by selecting it from the list on the Apps screen. Under your app's Domains tab, enter any domains or subdomains for the app both with and without the www., clicking Add after each one.
Be sure to add all of the domains that can be used to reach your app, even if you don't want the domain to be displayed in the URL. If you do not want one of your app's domains displayed, you can redirect it to the domain you do want shown; for example, redirecting www to non-www.