Having root-level access to your server means that you'll be able to view and modify any file on it, which includes essential system files. You may also install software which can modify certain settings on the server during the process, 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 will be able to do anything you want. You may also create various other users either with the same rights or with fewer rights, according to what you want them for - day-to-day tasks, other server administrators, etc. To be on the safe side, it is usually recommended to employ the root account only when you actually 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 connect to the server and to control it at the root level.