Having root-level access to a server signifies that you will be able to view and change any file on it, including essential system files. You may also set up software that can modify specific settings on your server during the process, so the installation can be performed only if you are logged in as the root user. The aforementioned has full privileges, which means that you'll have full control over the machine whenever you want and you will be able to perform anything you'd like. You may also create other users either with identical rights or with fewer rights, according to what you want them for - day-to-day tasks, other server administrators, etc. To be on the safe side, it's generally recommended to use the root account only when you really need it and not for tasks which can be done through 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.