When you have a few domains with different extensions and you want all of them to open exactly the same site, you can have the website under one of them and forward the others. There are various approaches to redirect one domain to another, such as the so-called domain parking. If your hosting package permits it, though, it'll 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 name is hosted, you could still have content for it, set up subdomains, e-mail addresses, and so on., while with a parked domain you are unable to do any of those things. For example, if you're building localized websites under different country-code domain names, you will be able to work on them, but in the meantime, visitors will be redirected to the main site.