An addon domain is a feature of a cPanel account where you can host more than one website on that specific cPanel account. cPanel is the interface that you will see when you log in to a hosting account.
How to setup an addon domain
LOGIN into your CPANEL account
In the section DOMAINS you will find Addon DOMAINS
Enter the new domain name
Example: newaddondomain.com
Subdomain will be automatically created as the new document root
Please also select the FTP option if you need it