Domain Registration is the act of acquiring a name on the internet for your website. It is necessary for a website to be seen others. One you register a domain name you keep the mentioned name at least one year and you can renew the registration each year endlessly.
There are many domain name registrar companies on the net. They offer .com, .net, .org and many other (Top Level Domains) TLDs. Actually a domain name is the combination of the numbers in order to be easy to keep in mind it is descripted with the letters.