To register your own nameserver:
- Click on Domain Manager and click the Change nameserver information icon next to the domain desired.
- Click on the Create Nameserver link at the top of the page.
- Enter your hostname and IP address for the nameserver and click Create Nameserver.
To modify name server:
- Go through the above step 1, 2, 3.
- Click on "Modify" link to the right of the nameserver and then replace the old IP with your new IP address.
- Click on "Modify Nameserver" button and submit the change.
IP address stands for Internet Protocol, this is the number your server or computer is assigned by the network you are on (xxx.xxx.xxx.xxx)
FQDN stands for Fully Qualified Domain Name which, essentially is the nameserver itself (ns.domainname.com)