A. An add-on domain is a fully functional domain that will work out of a folder in your main sites ftp.
Q. READ THIS BEFORE SETTING UP AN ADDON DOMAIN!
You cannot create an add-on domain if your dns hasn't proprograted to the server already. So after you change the sites dns you are trying to add you will need to wait 24-48 hours before attempting to create your add-on domain.
A. There are three fields cpanel asks for when creating an add-on domain.
1. "New Domain Name:" You will put in the newdomain.com do not put www in the name!
2. "Username/directory/subdomain Name:" This will be the folder cpanel creates in your main accounts ftp. MAKE SURE that the name you give it doesn't already have a folder. Example... If you want to give it the username chris. You cannot have a folder in your account named chris already. If you do and still try creating the username for the add-on domain to be chris you will mess a lot of things up!!!
3. "Password:" fill in any password you want here.
Q. Help I added an add-on domain why did it say subdomain added?!!?
A. It creates it as a subdomain by creating the folder within your main sites ftp. Please ignore this! It is a fully functional domain name. It is only called a subdomain when in fact it is an add-on domain.