The Name Servers of a domain name reveal the DNS servers that handle its DNS records. The IP of the site (A record), the mail server that takes care of the emails for a domain (MX records), any text record in free form (TXT record), forwarding (CNAME record) etc are taken from the DNS servers of the hosting provider and for any domain address to be using them and to be forwarded to their hosting platform, it ought to have their name servers, or NS records. If you want to open a site, for example, and you insert the URL, the browser connects to a DNS server, which keeps the NS records for the domain address and the request is then redirected to the DNS servers of the hosting provider where the A record of the website is obtained, allowing you to see the content from the proper location. Normally a domain has 2 name servers that start with NS or DNS as a prefix and the distinction between the two is simply visual.