Simply put, a domain name registrar is a service that allows you to officially register your desired website domain name so that it is unique to you, and no one else can own it. Originally, there was just one company that could register your domain name for you, but now there are literally hundreds.
Legitimate domain name registrars are accredited by the Internet Corporation for Assigned Names and Numbers (ICANN). ICANN is a private (non-government), non-profit corporation that has been given the responsibility of allocating IP addresses and managing the Domain Name System. The Domain Name System is what allows you to reach a website by typing in its name, rather than its numerical IP address. (For more on this topic, please read our article on "What Is a Domain Name?".)
What Domain Names Are Available to Register?

A "top-level domain" is the suffix that a domain name ends with, such as .com or .org. ICANN currently accredits domain name registrars for the following top-level domains:
Within any of these top-level domains, especially the popular .com and .net domains, many domain names have already been registered. Your domain name registrar will only allow you to register a domain name that has not yet been registered to someone else.

.aero (restricted to members of the aviation community)
.biz (restricted to businesses)
.com
.coop (restricted to cooperatives)
.info
.museum (restricted to museums and related persons)
.name (restricted to individuals)
.net
.org (restricted to non-profit organizations)
.pro (restricted to licensed professionals)

Do I Have to Work Directly with a Domain Name Registrar?
No. Although you can register your domain name directly with a dedicated domain name registrar, many web hosting providers, such as axonserver.com, can register your domain as part of their web hosting package. This is often a more economical option than registering your domain name independently and then choosing a web hosting company, as that often involves a transfer fee.