Having root-level access to a server means that you can view and modify any file on it, including essential system files. You may also set up software that can change specific settings on the server throughout the, so that 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 the machine at any time and you'll be able to perform anything you need. You can also create various other users either with similar rights or with fewer rights, depending on what you require them for - everyday tasks, other server administrators, etcetera. To be on the safe side, it's usually recommended to employ the root account only when you actually need it and not for tasks that you can do 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 control it at the root level.