Having root-level access to your server means that you can view and update any file on it, which includes crucial system files. You may also install software that can change particular settings on the server throughout the, so that the installation is possible only if you are signed 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 can perform anything you would like. You may also create various other users either with the same rights or with fewer rights, according to what you require them for - daily tasks, other server administrators, etc. To be on the safe side, it's usually recommended to use the root account only when you really need it and not for tasks you can do using 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.