1. Register the additional domain with a domain registrar
2. Set the nameservers at your registrar for that domain to point to your hosting provider's nameservers.
3. Login to cPanel and click "Addon Domains"
4. For "New Domain Name:" enter the domain you wish to add to your account.
5. Feel welcome to accept the defaults, just set the password for the FTP account.
6. You can upload pages by EITHER using those FTP credentials, or the FTP credentials for your main cPanel account.
I do not think this is answering the question. If someone used or uses other hosting control panels like Plesk of H-Sphere, there was always an option to add another domain to a hosting account as an end user in the control panel. This would create a new web folder for the site files and when you clicked on functions, liek to admin email, it would present you with your list of domains to select which one you want to admin the email for.
With cpanel it is confusing and this feature does not exist. When you "add-on" a domain it automatically adds it as a secondary domain in your web folder.
What I am doing right now is setting up each domain as a new user in WHM. I have multiple domains and I will add them this way and administer each having their own control panel. This is very clunky and I figure there MUST be a better solution in cpanel. I am a reseller, so I can do that and set up a private plan group to put them against. But, what is my end user supposed to do? Does anyone know how to effectively manage multiple TLDs in one cpanels hosting account interface?