Having root-level access to a server signifies that you'll be able to view and modify any file on it, which includes essential system files. You may also install software that can change particular settings on your server throughout the, so the installation can be done only if you're signed 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'll be able to do anything you need. You may also generate additional users either with similar rights or with fewer rights, according to what you require them for - day-to-day tasks, other server admins, etc. To be on the safe side, it is generally recommended to use the root account only when you really need it and not for tasks that you can do via other accounts. You may 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.