Having root-level access to a server means that you'll be able to view and update any file on it, which includes crucial system files. You can also install software which can modify specific settings on your server during the process, so the installation is possible only if you're logged in as the root user. The latter has full privileges, which means that you'll have full control over the machine whenever you want and you'll be able to do anything you want. You can also generate other users either with similar rights or with fewer rights, depending on what you need them for - everyday tasks, other server administrators, etcetera. To be on the safe side, it is generally recommended to employ 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 to connect to the server and to control it at the root level.