Having root-level access to a server signifies that you'll be able to view and modify any file on it, including essential system files. You may also set up software that can modify certain settings on your server during the process, so that the installation can be done only if you are logged in as the root user. The aforementioned has full privileges, i.e. you'll have full control over your machine at any time and you'll be able to do anything you need. You can also make various other users either with the same rights or with fewer rights, based on what you need them for - day-to-day tasks, other server administrators, etcetera. To be on the safe side, it's generally recommended to use the root account only when you really need it and not for tasks that you can do using other accounts. You can use a web-based graphical interface or a Secure Shell console to connect with the server and to manage it at the root level.