Having root-level access to a server signifies that you can view and modify any file on it, which includes essential system files. You may also install software that can change particular settings on the server during the process, so that the installation is possible only if you are logged in as the root user. The aforementioned has full privileges, i.e. you will have full control over your machine at any time and you can do anything you'd like. You may also generate additional users either with identical rights or with fewer rights, according to what you need them for - day-to-day tasks, other server admins, etcetera. To be on the safe side, it is usually recommended to employ the root account only when you really need it and not for tasks you can do through other accounts. You may use a web-based graphical interface or a Secure Shell console to connect with the server and to manage it at the root level.