Having root-level access to a server means that you'll be able to view and modify any file on it, including important system files. You can also set up software which can modify specific settings on the server during the process, so that the installation is possible 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 at any time and you'll be able to perform anything you need. You can also create various other users either with identical rights or with fewer rights, depending on what you need them for - everyday tasks, other server admins, etcetera. To be on the safe side, it's usually recommended to use the root account only when you actually need it and not for tasks that you can do through other accounts. You may use a web-based graphical interface or a Secure Shell console in order to connect with the server and to manage it at the root level.