I'm in the process of setting up my own name servers using BIND9, however I want to visualize the name server setup in relation to registrars and other name servers.

Say I have a domain www.mydomain.com

I setup my 2 name servers: ns1.mydomain.com -> 192.168.0.1 ns2.mydomain.com -> 192.168.0.2

1) How does the world know that my name servers are now at ns1.mydomain and ns2.mydomain. I read about setting up glue records at my registrar. Could you please elaborate on this, i.e. once i setup these glue records, can I now use my name servers in NS records for any other domain?

For e.g. NS records for www.otherdomain.com -> ns1.mydomain.com/ns2.mydomain.com

2) Given I setup the glue records as mentioned above, do I "have to" update mydomain.com NS records to point to my name servers? Can I keep mydomain.com NS records pointing to my registrars name servers, however use ns1.mydomain.com/ns2.mydomain.com as name servers for any other domain I own?

Thanks