I think you're badly misunderstanding how DNS work. NS records are used to find the authoritative server for a domain. The A resource record is what the client is requesting (normally) and is what will be looked up for the response to the client.
Lets say you own example.com. Someone enters http://www.example.com into their webbrowser. Their computer issues a recursive lookup for www.example.com to their local DNS server. That server doesn't know what IP www.example.com resolves to, so it figures out the lowest level of domain for which it does know the servers. In this case it's the
. root servers. The domain name
www.example.com is actually
www.example.com. <-- note the "." on the end.
So that DNS server contacts the root server and asks them if they know where www.example.com is. They don't. They do know where "com." is however, by was of NS records for that domain. This NS record is returned to the DNS server. So the DNS server contacts the "com." server and asks them if they know where www.example.com is, they don't either. But they do know where "example.com." is, again by NS records, which point to
b.iana-servers.net.. Nobody "just knows" where those servers are, so glue records for those domains are registered with the "net." root servers. More lookups to the "net." root servers...
The DNS server now knows how to contact the server for the
example.com. domain! So it asks that server if it knows where 'www.example.com' is, it does! That server has a SOA record that identifies it as authoritative for the 'example.com.' domain, and it knows the A record for 'www.example.com', the IP it points to. The DNS server returns this IP to the client and the world is safe for another night.
When the client requested
www.example.com from the DNS server it told the DNS server it was looking for an A record (A are for IPv4; clients also commonly look for IPv6 AAAA records too these days). When the other DNS server got the requests for the A record they also looked for CNAME records, but didn't search other record types. The DNS server know that when the request for a longer domain name fails (eg the root servers don't know where www.example.com is) that the DNS server is going to be interested in what information that server does have, eg. the NS record(s). How this works is more complicated than you'll care about, but the root server definitely returns a "failure" of sorts when the DNS server is trying to find the domain.
If the client was requesting a MX record for e-mail, or a SRV record, or a TXT record, or whatever, the responding DNS server will not just search for any record type that matches the domain name give, it will only search for the same record type (with the exception when looking for A or AAAA records the results for a CNAME match will be returned if no A or AAAA record matches). Also the server can have a "default" or wildcard records that may also match, but are subordinated to direct matches. It's best to avoid these situations unless you really know what you're doing.