There are two separate services that you need for a functioning site - a domain and a website hosting plan for it. If you type the domain name in your browser, you see the content that is uploaded in the website hosting account, but if that domain name is not linked to such an account or to an e-mail service, it's parked. To put it differently, the domain is registered and you are its owner, but it does not have any content of its own. Rather, it can open either a pre-made “Under Construction / For Sale” page from the registrar company, or it could be directed to some other URL of your choice. The main benefit of parking a domain name is that you can keep it and be sure that nobody else is going to take it. At the same time, it won't occupy a slot for a hosted domain within your account. You could also park domain names if you have a .com, for example, and you register domain addresses with other extensions like .net, .org or country-code ones to direct them to the main site so as to protect a brand name.