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 phone book tells people looking for your phone number that Company A's Phone number is xx-xxx-xxx, just as a domain tells people (i.e. their computers) domainA.com is hosted on the server xx.xxx.xx.xxx. Without the domain, you would have to tell your customers “Hey my site is located at "13.456.79.123/~mysite/" instead of "mysite.com". You can see how, without a domain, having a site or hosting is a lot of stress.
The web-hosting or server portion is much like the space that you rent out to have your business in. It is merely the space itself. It does not include furnishings like shelves for your products, just as the web-hosting account does not include a site for you to sell your products. Luckily, in the web-hosting world, it's very easy to furnish the space provided by your host, because you can install many framework applications through the softaculous app within your cPanel, CWP, DIrectAdmin or other control panels. Without the hosting services, you will not have a place for your files to reside, so your domain would then become like a disconnected phone number in the phone directory, and your site files would have nowhere to stay.
