Parked Domains are often used by users who would like to display the same website on multiable domains, it can also be used used for email addresses.
Domains must be registered before they can be parked onto your account. In addition the domain will not be functional unless it is configured to point to the same name servers as your primary domain.
To Add a parked domain to your account:
Log into cPanel you can get to this through http://yourdomain.com.au/cpanel
Once you have logged in, in the Domains Section, Left Click the "Parked Domains" icon
Under "Create a New Parked Domain", enter the domain name you would like to park on top of your primary domain then left click "Add Domain"
Once this is done you have Successfully Parked a domain