Having root-level access to a server signifies that you can view and modify any file on it, which includes essential system files. You can also install software that can modify specific settings on the server throughout the, so the installation can be done only if you are logged in as the root user. The aforementioned has full privileges, i.e. you will have full control over the machine whenever you want and you will be able to perform anything you want. You can also make various other users either with the same rights or with fewer rights, based on what you require them for - everyday tasks, other server administrators, 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 which can be done via other accounts. You can use a web-based graphical interface or a Secure Shell console to be able to connect with the server and to control it at the root level.