Click on the Domain Aliases icon.

 

Here HELM will display the Domain Aliases that are set up for the domain. For this domain, there are not currently active. Click Add New to create a new one.

 

Domain Alias Name 
The domain alias name is the full domain name that will alias the main hosted domain for this account. When connecting to the domain alias name through a web browser, you will see the same website as the main hosted domain.

Main Domain 
The main domain is the main hosted domain for this account. This is the domain for which the alias has been set up for.