When you have several domains with different extensions and you need all of them to open the same website, you can have the Internet site under one of them and forward the others. There are various approaches to forward one domain name to another, among them the so-called domain parking. If your website hosting plan allows it, though, it shall be better if you host all the domains and set up a URL redirect, not a domain redirect. The difference between the two is that while a domain is hosted, you can still have content for it, set up subdomains, e mail addresses, and many others., while with a parked domain it's not possible to do any of those things. As an example, if you are building localized sites under various country-code domain names, you'll be able to work on them, but at the same time, visitors shall be forwarded to the primary website.