Having root-level access to a server means that you can view and change any file on it, including important system files. You may also install software that can modify specific settings on your server throughout the, so that the installation can be performed only if you are signed in as the root user. The latter has full privileges, i.e. you'll have full control over the machine whenever you want and you will be able to do anything you'd like. You may also generate various other users either with the same rights or with fewer rights, based on what you want them for - day-to-day tasks, other server admins, etc. 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 can be done using other accounts. You may use a web-based graphical interface or a Secure Shell console to be able to connect with the server and to manage it at the root level.