Every domain on the Internet requires a way to be found on the Internet. The first step in the process is registering the domain name you would like with a registrar. Through the registrar, you can identify which name servers are responsible for DNS. These name servers then have the authority to resolve your website.
If you've registered your domain name through XMission, and we are also hosting your website, you shouldn't need to update your name server information. By default, any domain name registered through XMission automatically points to our name servers.