About the tool
This tool finds out the the name servers a given domain name. Nameservers tell the world, the ip address of a given domain (xyz.com). The nameservers must be up for a domain name to be discovered on the internet. If the nameservers are down, then the domain's ip address would not be found and the domain would not be reachable. Browsers would say "Website not found".
To open a website browser contacts the DNS servers, and the dns servers contact the nameservers.