A domain name is your personal or business home on the Internet, it’s a piece of online real estate that you control completely—as long as you own the rights to that name.
In order to claim it for your exclusive use and to share it with the online world, you must register it with a qualified domain registrar. Most professional web hosting services (like Namecheap) are also a qualified domain registrar.
If they already took the domain name you want, you won’t be able to use it for your own site.
A domain name has two parts; the first part is the name of your website, the last part of a domain name we call it the ‘extension’.