Firstly register a new domain:
Make sure you have a new domain registered to host to your Hostgator account. Please be aware that Hostgator charges $15 for a new domain registration. It is higher compared to the market so you can register through a different company like, “Go Daddy.”

Name Servers set up:
Now you need to change the name server entries for that particular domain. The name servers should be set to your Hostgator name servers. You’ll get the information for your Hostgator name servers by login into your account.
Adding the new Domain in Hostgator cPanel:
• Login to your cpanel
• Go to domain section
• Click on Addon Domains
• Enter new Domain and ftp username
• Choose your document root e.g. /yourdomainname.com
• Set your passwords.
• Click on Add Domain