In case you have a number of domains with different extensions and you need all of them to open exactly the same site, you could have the website under one of them and redirect all the rest. There are a number of approaches to redirect one domain to another, among them the so-called domain parking. If your hosting package deal permits it, though, it will be better if you host each of the domains and create a URL redirect, not a domain redirect. The main difference between the two is that while a domain address is hosted, you may still have content for it, create subdomains, e mail addresses, and many others., while with a parked domain it's not possible to do any of those things. For example, if you are building localized websites under various country-code Internet domain names, you will be able to work on them, but in the meantime, visitors shall be redirected to the main site.