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.
Your primary domain name's root directory is the root of the hosting account, which can be symbolized as a single forward slash (i.e. "/" without the quotation marks), or as an entirely blank field.
Secondary and subdomain names' root directories were specified when they were set up. You can find them listed in the Hosting Control Panel.
To Find Secondary and Subdomains' Root Directories
Secondary domain names' root directories display in the Folder field.
To find a subdomain's root directory, click the "parent" domain name. All of that domain name's subdomains display, along with their root directories in the Folder field.