Having root-level access to a server means that you'll be able to view and update any file on it, which includes crucial system files. You can also set up software which can update certain settings on your server throughout the, so the installation is possible only if you are logged in as the root user. The latter has full privileges, which means that you will have full control over the machine at any time and you can do anything you want. You can also make various other users either with identical rights or with fewer rights, depending on what you need them for - everyday tasks, other server admins, etcetera. To be on the safe side, it's generally recommended to employ the root account only when you really need it and not for tasks you can do through other accounts. You may use a web-based graphical interface or a Secure Shell console in order to connect to the server and to manage it at the root level.