The NS, or Name Server records of a domain name, show which servers manage the Domain Name System (DNS) records for it. Setting the name servers of a specific host company for your domain address is the most convenient way to forward it to their system and all its sub-records will be handled on their end. This includes A (the IP address of the server/website), MX (mail server), TXT (free text), SRV (services), CNAME (forwarding), etc, so if you wish to modify any one of these records, you'll be able to do it using their system. To put it differently, the NS records of a domain name show the DNS servers that are authoritative for it, so when you attempt to open a web address, the DNS servers are contacted to retrieve the DNS records of the domain name you are trying to access. That way the site that you're going to see is going to be retrieved from the right location. The name servers typically have a prefix “ns” or “dns” and every single domain name has at least two NS records. There is absolutely no sensible difference between the two prefixes, so what kind a web hosting provider is going to use depends only on their preference.