Depending on your EverWeb + Hosting account you can host from 5 to unlimited domains on your account.
These additional websites are known as add-on domains. Once you have the domain registered, it still needs to be added to your account as an add-on domain in order for it to appear in the Domains drop down menu on EverWeb's Site Publishing Settings window. Watch this video tutorial to learn how to add an add-on domain to your account.