When you have a number of domains with different extensions and you want all of them to open the exact same site, you can have the website under one of them and forward all the rest. There are various ways to forward one domain name to another, like the so-called domain parking. If your web hosting plan allows it, though, it shall be better if you host all of 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 could still have content for it, create subdomains, e mail addresses, and so forth., while with a parked domain you cannot do any of those things. For instance, if you're building localized websites under different country-code Internet domain names, you shall be able to work on them, but meanwhile, visitors will be forwarded to the primary website.