You need to add a new binding for your site in IIS. More information could be found in our Sitefinity documentation.
After that when a new site is created you need to specify its domain. Please refer to this article
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Sitefinity CMS Ideas&Feedback Portal
and vote to affect the priority of the items