Having root-level access to your server means that you can view and modify any file on it, which includes essential system files. You can also install software that can modify particular settings on your server during the process, so the installation can be performed only if you are signed in as the root user. The latter has full privileges, which means that you will have full control over your machine whenever you want and you can do anything you want. You may also generate additional users either with similar rights or with fewer rights, according to what you need them for - daily tasks, other server admins, 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 which can be done via other accounts. You may use a web-based graphical interface or a Secure Shell console to connect with the server and to control it at the root level.