First go to your client area and click the "Domains" drop down then click "My Domains":
Second click the "Manage Domain" button on the domain name you want to use:
Third set your domain nameservers to our registrar default nameservers so we can mange the DNS records:
Set the nameservers to the following three and save:
Fourth now we need to go to the "Manage DNS" page under the Management Tools tab:
Fifth we can set our DNS entries here to point the domain to your server IP:
Under the 'Address' field enter your server IP address (no port! If you don't have port 25565 open a ticket to have one assigned.)
Under the 'Host Name' field leave it blank if you want players to connect using the root domain, such as testdomain.com. If you want them to connect using a sub-domain such as 'play.testdomain.com', enter 'play' into the host name field, then click Save Changes.
DNS changes can take a couple of hours to take affect, so wait patiently and it should work properly.