Locate and click on the “Addon Domains” icon under the “Domains” category.

Enter the required information:
New Domain Name – The domain name you are addin to your account.
Subdomain/FTP Username – Create a login name for the new domain.
Document Root – Folder within the master domain’s root directory to hold files for the new domain.
Password – Password for the user defined above.
Password (Again) – Confirm the password.

Click the “Add Domain” button to create the addon domain.
Note: This will only work if the addon domain’s DNS servers are set to the same as the master domain’s.