If you have a few domains with different extensions and you would like all of them to open exactly the same site, you could have the website under one of them and forward the others. There are a number of approaches to redirect one domain to another, including the so-called domain parking. If your website hosting package deal allows it, though, it will be better if you host all the domains and create a URL redirect, not a domain redirect. The primary difference between the two is that while a domain name is hosted, you may still have content for it, create subdomains, email addresses, and so on., while with a parked domain you can't do any of those things. For instance, if you're building localized websites under different country-code domain names, you'll be able to work on them, but meanwhile, visitors shall be forwarded to the primary website.