Having root-level access to your server means that you'll be able to view and modify any file on it, including essential system files. You can also set up software which can update particular 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, which means that you'll have full control over the machine at any time and you will be able to perform anything you want. You can also make other users either with identical rights or with fewer rights, according to what you require them for - daily tasks, other server admins, etc. To be on the safe side, it's usually recommended to employ the root account only when you really need it and not for tasks you can do via other accounts. You may use a web-based graphical interface or a Secure Shell console to connect to the server and to control it at the root level.