If you want to register a domain to make certain that nobody else will take it, but you haven't created the site for it yet, you may park it. That is a service that registrar companies offer if a domain address is not connected to any web or email hosting service. In this way, you are able to protect a brand name, for instance, and you will own the domain in question although it won't load any content. If you want, you can select some standard template that the registrar provides, like For Sale or Under Construction, you can also forward the domain name to a new web address. Your second option is very helpful in case you own a number of domains, but you want every one of them to open the same website. As an example, you could register domain.net and domain.org, then park them and forward them to domain.com. In this example, you'll need hosting for the third domain address only and the traffic to the other ones will be redirected to it.