If you have purchased your domain elsewhere you will need to update your name servers to point to your hosting account on our servers.
Please read your welcome e-mail. If you have lost your welcome email you can email support for your server's DNS information.
Whatever name servers are listed in your welcome email will be the ones to use for all of the sites you choose to host out of your account.
The section on your welcome e-mail you are looking for will look like this:
New Account Info
Server IP: 220.127.116.11
Nameserver 1: ns1.leadingwebexposure.com
Nameserver 2: ns2.leadingwebexposure.com