When you register a domain name, it does not know which site on the internet it points to. You need to change a setting to tell it where to point. This setting is called the "Name Servers". No matter who you use for a registrar, the process is roughly the same - you log on to their site, you edit your domain name, and you change the name servers to:
The spot where you can update this information varies from registrar to registrar. You'll want to consult their help documents or support team for specific information if you can't find it yourself.
It's important that you make sure that your email accounts are set up on our end soon before making this change. You can set this up using the "Domain/Email" item of your "Features" menu. If you do not yet have access to this, it will be available soon.