Having root-level access to a server means that you'll be able to view and update any file on it, including essential system files. You may also install software that can modify certain settings on the server during the process, so that the installation can be done only if you're signed in as the root user. The latter has full privileges, which means that you will have full control over the machine whenever you want and you can perform anything you'd like. You can also generate various other users either with the same rights or with fewer rights, based on what you need them for - everyday tasks, other server admins, etcetera. To be on the safe side, it's 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 can use a web-based graphical interface or a Secure Shell console to connect with the server and to control it at the root level.