Having root-level access to your server means that you can view and modify any file on it, including essential system files. You may also install software which can change particular settings on your server throughout the, so the installation can be performed only if you're logged in as the root user. The latter has full privileges, i.e. you'll have full control over the machine at any time and you can perform anything you want. You may also generate additional users either with the same rights or with fewer rights, depending on what you need them for - daily tasks, other server administrators, etcetera. To be on the safe side, it is usually recommended to use the root account only when you actually need it and not for tasks that you can do through other accounts. You can use a web-based graphical interface or a Secure Shell console to connect to the server and to manage it at the root level.