In case you have several domains with different extensions and you need all of them to open the same website, you can have the website under one of them and forward all the rest. There are a number of methods to forward one domain to another, among them the so-called domain parking. If your website hosting package permits it, though, it shall be better if you host all the domains and create a URL redirect, not a domain redirect. The main difference between the two is that while a domain is hosted, you can still have content for it, set up subdomains, email addresses, etc., while with a parked domain you are unable to do any of these things. For example, if you're building localized websites under several country-code Internet domain names, you shall be able to work on them, but at the same time, visitors shall be forwarded to the main Internet site.