If you have a registered domain, then somewhere on your registrar's site you should be able to login to your account and set the domain nameserver addresses. These addresses are the DNS servers that will be the authoritative DNS servers for your domain. These can be public DNS servers from your domain host, or from a company like easydns.com.
If you want to run your own nameservers, you'll set the public ip addresses you have for your dns servers. This could mean you have to setup port forwarding, etc. In reality, if you don't have public IPs then I would not try to host DNS yourself. If this is a learning experience then have at it, but I personally use easydns.com for my domains.
hope that gives you a bit of a start
