Enter into the box at Register.com the domain name in which you have an interest,
check the box next to the extension you want, usually .com,
and press "go".
On the page that appears, search for the name you wanted
with the extension you prefer, generally ".com".
If the name you want is available, you can register it yourself.
If the name is unavailable, click on "view WHOIS".
You will see information about the person or organization to whom the domain name is registered. There may be notations that the name is for sale, with an email address to use to discuss possible purchase of the domain name.