Domain Name:

Domain name is a name people use to reach your website or Blog just like www.Blogginggame.com is a Domain name and you reach Blogging game by entering that URL in your browser’s Web Address Bar.
You can register a Domain name by going to any Domain name registrar’s website and choosing a domain name and yes you if that name is already registered you have to choose another one.
After registering a Domain name you have to change its DNS settings according to your Web Host Server’s DNS setting, after DNS setting will take effect you will be able to work on your website.