What is multiple domain hosting and subdomains?
With multiple domain hosting you can use the same account with a host for two domains or more. Lets assume that you have registered two domains: www.m-6.com and www.6-m.com. With multiple domain hosting you will be given one directory/folder on your webhost server where you would upload your HTML files/pages.But the webhost company will configure your website so that if someone types m-6.com or 6-m.com into their web browser, that person will be taken to the one and same site. In other words, both domain points to your one web account on your server.

Subdomains are the third level domains in the sense they are used to organise your website content. They are just folders under your root directory but to access them a special url is used.
For instance, http://www.m-6.com is a regular URL without a subdomain.
http://features.m-6.com is an URL with subdomain"features".
Here the
.com is the first level domain
m-6 is the second level domain
features is the third level domain