After entering the Domain manager and selecting a domain name. Use the lower menu pictured above to add new NS records for your domain.

 

The Add new NS records screen.

Enter a name, and your servers IP address.

 

After you have created new NS records for your server update your domains DNS servers to use these records.

 

 These simple screenshots should aid the process of registering your server as a name server. If in doubt ask your registrar. Explain you must host your own DNS. They should have help files available for use.