There are many registrars to choose from . I've heard well of AW Registry but haven't tried them yet. A registrant is allowed to create third level domain names like maine.greens.org . Type a domain name in the box and click the button. Whois info is not always reliable.
Nobody checks whether the registrant told the truth.
A computer that tells everybody's software what a domain name means is called a name server . ZoneEdit has a picture of how it works . To get an idea what that means, you can try mine. Most companies that do Web service do name service, too. The name server that's responsible for your second level domain name is said to be authoritative for your zone .