Login to cPanel.
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.
