The Name Servers of a domain show the DNS servers that are responsible for its DNS records. The IP of the website (A record), the mail server that manages the e-mails for a domain (MX records), any text record in free form (TXT record), pointing (CNAME record) etc are obtained from the DNS servers of the web hosting company and for any domain address to be using them and to be directed to their hosting platform, it needs to have their name servers, or NS records. If you wish to open a website, for example, and you enter 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 webhosting provider where the A record of the site is obtained, so you can see the content from the proper location. Commonly a domain name has two name servers that start with NS or DNS as a prefix and the difference between the two is just visual.