Having root-level access to a server means that you can view and change any file on it, including crucial system files. You may also install software which can modify particular settings on the server throughout the, so the installation can be done only if you're signed in as the root user. The aforementioned has full privileges, which means that you will have full control over your machine at any time and you'll be able to do anything you need. You may also generate additional users either with similar rights or with fewer rights, based on what you want them for - everyday tasks, other server administrators, etcetera. 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 via other accounts. You can use a web-based graphical interface or a Secure Shell console in order to connect to the server and to control it at the root level.