Having root-level access to a server signifies that you'll be able to view and modify any file on it, which includes important system files. You may also install software that can update particular settings on the server throughout the, 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 whenever you want and you'll be able to perform anything you want. You can also create other users either with the same rights or with fewer rights, according to what you need them for - daily tasks, other server administrators, etcetera. To be on the safe side, it is usually recommended to use the root account only when you really need it and not for tasks which can be done through other accounts. You may use a web-based graphical interface or a Secure Shell console to connect to the server and to control it at the root level.