How do other DNS servers find mine?

How do other DNS servers find mine?

I'm trying to learn as much as possible about DNS, and so far I've read
most of:
http://www.zytrax.com/books/dns/ch8/soa.html
and all of:
http://computer.howstuffworks.com/dns.htm
I understand that SOA and NS records contain info about the authoritative
name server for a domain, but as these are just DNS records, how does the
rest of the world even know where to get them?
I assume it starts at the top-level-domain (.COM .NET .ORG, etc) servers.
So they must contain a SOA record for my domain? If so, how does that get
there? I imagine only registrars like GoDaddy and Network Solutions are
able to update those? If they contain a SOA record, why does my DNS server
(that I host), need one also? I think there must be something, maybe in
the domain registration records (outside of DNS?), that I'm missing.
I think I've got a pretty good understanding of most parts of the DNS
system, after reading lots of articles.. but I haven't found any that
answer this part, in a way that I understand it.
For example, GoDaddy and Network Solutions both let me change different
options (in their web UI) to "host my own DNS server". If these options
remove them from the process, so DNS servers never need to query them
again, and instead query my server directly (this is what I want, no
dependency on GoDaddy/NS)... when I make these changes, what (at the DNS
level or otherwise) is GoDaddy/NS doing? Are they asking the
top-level-domain servers to update some DNS records for my domain?