How to ADD the ADDON domain:
1: Login to your cpanel.
2: There under the section of " DOMAIN" you will find the option "ADDON DOMAINS", click on it.
3:Once you click there a new tab will open then under "CREATE AN ADDON DOMAIN", add your domain name at place of "New domain name" the "subdomain section" and "documentation root" will be filled automatically once you click on "ADD DOMAIN".
4:Once you click on the "ADD DOMAIN" addon domain will be added in your panel now you can host your website in your root folder of addon domain.
**Once you ADD the ADDON domain then you can install the wordpress similarly as you have installed for your primary domain ,Please click here to check how to install the wordpress.**