If you have several domains with different extensions and you want all of them to open the same website, you may have the website under one of them and forward the others. There are various ways to forward one Internet domain name to another, such as the so-called domain parking. If your hosting plan permits it, though, it shall be better if you host each 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 may still have content for it, create subdomains, email addresses, and so on., while with a parked domain you are unable to do any of those things. As an example, if you're building localized Internet sites under various country-code Internet domain names, you'll be able to work on them, but meanwhile, visitors shall be redirected to the main website.
