If you have a number of domains with different extensions and you need all of them to open the exact same site, you could have the site under one of them and forward the rest. There are different methods to redirect one domain name to another, among them the so-called domain parking. If your web hosting package deal permits it, though, it shall be better if you host all the domains and set up a URL redirect, not a domain redirect. The real difference between the two is that while a domain is hosted, you can still have content for it, create subdomains, e-mail addresses, etc., while with a parked domain you are unable to do any of those things. As an illustration, if you're building localized Internet sites under several country-code domain names, you'll be able to work on them, but at the same time, visitors will be redirected to the main Internet site.