Having root-level access to a server means that you can view and modify any file on it, which includes crucial system files. You may also set up software that can update specific settings on your server during the process, so the installation is possible 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 perform anything you want. You may also make other users either with identical rights or with fewer rights, based on what you require them for - day-to-day tasks, other server administrators, etcetera. To be on the safe side, it is usually recommended to use the root account only when you really need it and not for tasks that can be done via other accounts. You can use a web-based graphical interface or a Secure Shell console in order to connect to the server and to manage it at the root level.