Having root-level access to your server signifies that you can view and change any file on it, including essential system files. You can also set up software that can modify particular settings on the server during the process, so that 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 your machine whenever you want and you'll be able to do anything you want. You can also create additional users either with the same rights or with fewer rights, based on what you want them for - everyday tasks, other server admins, etc. To be on the safe side, it's generally recommended to employ the root account only when you actually need it and not for tasks which can be done using 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 manage it at the root level.