Having root-level access to your server signifies that you'll be able to view and modify any file on it, including crucial system files. You may also install software which can change specific settings on the server throughout the, so that the installation is possible only if you're logged in as the root user. The latter has full privileges, i.e. you'll have full control over your machine at any time and you can perform anything you need. You may also make additional users either with similar rights or with fewer rights, depending on what you require them for - day-to-day tasks, other server admins, etcetera. To be on the safe side, it's generally recommended to use the root account only when you actually need it and not for tasks that you can do via other accounts. You can use a web-based graphical interface or a Secure Shell console to connect with the server and to control it at the root level.