I don't understand about roots, but the other stuff made sense.
The hard drive has many folders, and folders within folders. For example, one of the folders is Applications and it has all your applications in it. Since the Applications folder is not within any other folder, it is said to be at the
root of the drive. The applications inside it are not root folders, therefore. Other root folders are Library, System, Users, and Shared. You may have more that I didn't mention, but if you double-click your hard drive icon to see what's inside, any folder that has not been opened is a root folder.
