When you have several domain names with different extensions and you need all of them to open the very same website, you could have the website under one of them and forward the others. There are a number of methods to redirect one domain to another, among them the so-called domain parking. When your hosting package permits it, though, it shall be better if you host each of 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, and many others., while with a parked domain you can't do any of those things. As an example, if you're building localized sites under different country-code domains, you will be able to work on them, but at the same time, visitors shall be forwarded to the main Internet site.