1. First you need to Log in to your Cpanel control panel. 

2. Once logged into the Cpanel control panel you can set up your domains hosting.

To add a new domain go to Account Functions – Create a New account.

3. Enter in the new domain name. Specify a Username and Password (Make a note of these and keep in a safe place.) then set the Service Plan to Unlimited and hit OK
If you’re using an external mail host IE. Gmail, Office 365, Yahoo, etc then you will also need to select Remote Mail Exchanger which as at the bottom of the account creation page:

4. That's it! Your new domain has been added into your VPS and you can now go ahead and configure it as necessary.