In case you have a number of domains with different extensions and you want all of them to open exactly the same website, you can have the site under one of them and redirect the others. There are a number of approaches to forward one domain name to another, like the so-called domain parking. When your 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 name is hosted, you can still have content for it, set up subdomains, e-mail addresses, and so forth., while with a parked domain you cannot do any of these things. As an example, if you are building localized websites under various country-code domains, you'll be able to work on them, but meanwhile, people shall be forwarded to the primary website.