The root directory of your website is the content that loads when visitors access your domain name in a Web browser. The most obvious consequence of this is that you need to put your "index file" in your website's root directory for visitors to see your site at all.
Website-related applications might also need to know your website's root directory.
Your website's root directory depends on whether the domain name is your primary domain name or another type.
The root directory displays in the Document Root field.