Having root-level access to a server signifies that you'll be able to view and change any file on it, which includes crucial system files. You may also install software which can change certain settings on your server throughout the, so that the installation can be done only if you are logged in as the root user. The aforementioned has full privileges, which means that you will have full control over the machine whenever you want and you can do anything you would like. You may also create additional users either with the same rights or with fewer rights, depending on what you need them for - day-to-day tasks, other server administrators, etcetera. To be on the safe side, it's usually recommended to employ the root account only when you really need it and not for tasks which can be done through other accounts. You may use a web-based graphical interface or a Secure Shell console to be able to connect to the server and to manage it at the root level.