In case you have a few domain names with different extensions and you would like all of them to open the same website, you could have the site under one of them and forward the others. There are various approaches to redirect one domain name to another, like the so-called domain parking. If your website hosting package permits it, though, it shall be better if you host all of the domains and set up a URL redirect, not a domain redirect. The main difference between the two is that while a domain address is hosted, you can still have content for it, set up subdomains, email addresses, etc., while with a parked domain it's not possible to do any of those things. For instance, if you're building localized Internet sites under various country-code domains, you'll be able to work on them, but at the same time, visitors will be redirected to the primary Internet site.