Step 3: Associate the DNS Server with Registrar
Once you've setup your dns server you should go back to the registrar you registered your domain with and find the account management area of the site.
Once logged in there will be options for editing your domain registration record with details about the owner, contacts, nameservers, etc.
The image below is the domain management tool for domain-zone.net fill out fields on your registrar's control panel to match the settings below.