In case you have a few domains with different extensions and you would like all of them to open exactly the same website, you could have the site under one of them and redirect the others. There are different ways to redirect one domain to another, such as the so-called domain parking. When your website hosting plan permits it, though, it will be better if you host each of the domains and create a URL redirect, not a domain redirect. The difference between the two is that while a domain is hosted, you may still have content for it, create subdomains, e-mail addresses, and so on., while with a parked domain you cannot do any of these things. As an example, if you are building localized sites under various country-code domain names, you will be able to work on them, but in the meantime, people shall be forwarded to the primary website.