I`m just reading up on DNS and NS records, and while I have found lots of description of what they are, there's none saying in what situation you would need to specify one.
I have only ever dealt with 'flat' networks so multiple DNS servers have never been needed (i`m assuming this is where you would use NS records) some tell me if i`m wrong though!
They are created automatically when you make your zone(s). In a nutshell, they specify the name servers for your domain. You can add to the list manually if you want to delegate zones.
Suppose you owned 'bugs.co.uk'
If you wanted a subdomain called 'mystuff.bugs.co.uk' you would create NS records for 'mystuff.bugs.co.uk' in 'bugs.co.uk'. The NS records must point to the DNS servers responsible for 'mystuff.bugs.co.uk' .
For simple delegations, the NS records can point to the same DNS servers for 'mystuff.bugs.co.uk' and 'bugs.co.uk'. They don't have to be different, but uk.ibm.com and us.ibm.com are very likely to be different.
Something like that, anyway.