you need to remember where Linux's roots are (networking OS). The root password allows one person to control everything on the box, and subsequent user passwords allow almost any number of other "ordinary users" to use the system, but without the ability to mess things up. Normal users are typically restricted in the folders and files they can access, and the admin tools that they can use. Root controls who has access to what and root has access to everything. This is why it is never a good idea to be logged on as root when connected to the internet. You should normally set up a root account to adminster your system, and a user account for yourself, to actually do your work with.