1) Login to your Control Panel (cPanel) account with your username and password.
2) Under Domains, click on Addon Domains
3) Here you can key in new domain name details accordingly.
There are FOUR(4) fields cPanel asks for when creating an Addon Domain.
1. "New Domain Name:" You will put in the domain.com without put www in the name!
2. "Subdomain:" This will be use for addon/subdomain FTP account username.
3. "Document Root:" This will be the folder cPanel creates in your main FTP accounts.
4. "Password:" fill in any password you want here.
4) Click "Add Domain" button to confirm your latest changes.