The domain name is much like an entry in a phone book. Computers communicate by using numbers, called IP addresses, to contact each other, much like you use a phone number to dial a specific person's phone. If you want people to find your business's phone number, you want to be listed in a phone book. The web-hosting or server portion is much like the space that you rent out to have your business in. It's merely the space itself. you have a site visitor, who goes to your domain name, which translates into your server IP address, then the server sends that user your site files, which their browser represents to them as a typical 'web-page'. You can see that, without each of these 3 elements, you won't really have a 'web-site'.