What is a domain name?
A domain name is basically your identity on the internet. It is like your name and address all in one. Without domain names, the only way to get around the internet would be by using IP addresses, and it is much more difficult to remember a set of numbers like 220.127.116.11 than it is mydomain.com. Computers work well with numbers, people work well with words. Domains are used for websites and also for email. Your website might be mydomain.com, and your email might be firstname.lastname@example.org. In both examples, the "mydomain.com" is the domain name.
Aren't domain names supposed to have "www" in them?
An actual domain name does not have a "www" in it. The "www" part is often used with the website of a domain, but is not part of the actual domain itself. When you register a domain, you register it as "mydomain.com" only, but your website might be www.mydomain.com (or it may just be mydomain.com or both may in fact work).
How do I find who my domain is registered through?
The company that a domain is registered through is known as a domain registrar. A domain registrar can be found by performing a whois lookup on the domain. There are many sites that provide a whois lookup. One website that can do this can be found here. On this site you can type the domain name into either the "Domain Info" field or the "Whois Lookup(Domain)" field. For a .org site you usually have to go to pir.org and enter in the .org domain there to get any information on the registrar. Here is an example of the registrar on a whois.
What is a Whois listing?
A Whois listing contains information about the owner of a domain and other information associated with the particular domain such as when it was first registered and when it expires. It is important that the information listed in the Whois is up to date and valid. The administrative contact in particular needs to remain valid and is used when information needs to be sent to someone at the domain or for other tasks such as transferring a domain to a different registrar.
What is the difference between a .com, a .net, a .org etc?
These days there is not that much difference between a .com, a .net or any other domain extension. Originally they were used to differentiate between what the domain was being used for. .com was for businesses (commercial) .net was for a technology based business and .org was for non-profit type organizations. Now many companies and individuals will register a .com, a .net and a .org domain all at once to protect their own interests.
What is a subdomain?
A subdomain adds an extra level to a domain name. If you have a domain of "mydomain.com" then a subdomain of that might be "corporate.mydomain.com". Subdomains are commonly used to assign unique names for a particular part of a network or website. A company might have a public website that uses the main domain, and then a company only section of the website that uses a subdomain.