When you register a Domain Name you do so with a Registrar. You may or may not use that Registrar to Host your site.

Most Registrars will provide a small amount of web space on their web server to show a page that tells any visitors to your Domain that the site has been registered and is awaiting a web site.

The NameServer directs the site visitor to the location of the Web Host that is hosting your site. So when you register the Registrar sets the NameServer to point to their own server. If you do not use the Registrar to host your site you will need to change the NameServers to point to the location of your web host. This address will be made available after you sign up with a web host.

A NameServer address is in the form of ns1.registrarsitename.co.uk