Having root-level access to a server signifies that you'll be able to view and change any file on it, which includes important system files. You may also install software which can update specific settings on your server throughout the, so that the installation can be done only if you are signed 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 will be able to perform anything you'd like. You may also make other users either with the same rights or with fewer rights, depending on what you need them for - day-to-day tasks, other server admins, etcetera. To be on the safe side, it's usually recommended to use the root account only when you actually need it and not for tasks that can be done using other accounts. You can use a web-based graphical interface or a Secure Shell console to connect to the server and to control it at the root level.