When it's time to register your new web site, the first thing you need to do is pick the right name. Once you have your name, you need to make sure that domain is available. There are several web sites you can visit to check this, but rather than spending the time to do that individually, you can do it all in one place... the Network Utility.

Using the Network Utility is simple. Open it (Applications | Utilities), then click on "Whois". From here, all you need to do is enter the domain name, and choose the whois server you would like to use (you will find that they give you generally the same information). Below is a sample query:

You can see that the above search resulted in a "No match found" response, which means that this domain is available for registration. If the domain were already registered, it would give you contact information for the registrant.