An addon domain is a fully functional domain that will work out of a folder in your hosting account.
When you have another domain and wish to add the domain into existing hosting (cPanel)
kindly login to cPanel hosting, then go to Addon domains
then fill out the on those fields
1. “New Domain Name:” You will put in the domain.com without put www in the name!
2. “Subdomain/Ftp Username:” 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 (optional).
then click Add Domain