Domain Name Registration
In the past, there was only one place where you could register a dot-com domain.
(From now on, when we talk about a domain name, we'll simply assume that it is a dot-com domain, since it is the TLD that many people prefer.)
Nowadays, there are several "registrars" where you can register your domain; prices range from less than $10 to more than $30 per year.
You don't have to deal with registrars directly; most web hosts will gladly register a domain on your behalf (they usually make a small profit on it).
On the sites of most web hosts, you will find a comparison of their hosting packages. You will sometimes see: "Your Own Domain", or something similar.
This does not always mean that the annual domain name registration fee is included in the listed web hosting fee.
It may simply mean that you have the right to use your own domain, instead of having to use one of the available alternatives.
Always double-check with the host before you sign up!