Having root-level access to a server signifies that you will be able to view and modify any file on it, including essential system files. You may also set up software which can update particular settings on your server during the process, so the installation is possible only if you are signed in as the root user. The aforementioned has full privileges, which means that you'll have full control over the machine at any time and you'll be able to perform anything you want. You may also create other users either with the same rights or with fewer rights, according to what you require them for - everyday tasks, other server admins, etc. To be on the safe side, it is usually recommended to employ the root account only when you actually need it and not for tasks that you can do through other accounts. You can use a web-based graphical interface or a Secure Shell console to be able to connect to the server and to control it at the root level.