The addon domain menu lets you to add extra domains as addon domains to your hosting account.
An addon domain allows you to link that domain to a subdomain of your main domain. This lets you host additional domains from your account.
1 Click on the icon above the words Addon Domains on the main screen.
2 Enter the name of the addon domain in the blank field next to New Domain Name
3 Enter the name of the directory that will contain the files for the subdomain that the addon domain will be pointed to, in the blank field next to Username/directory/subdomain Name
4 Type in the password for the new addon domain, and click on Add Domain!
Addon domains will need to be registered with a valid domain name registrar before they can be added. Make sure that your account has the ability to use addon domains before attempting to add one.