Having root-level access to a server signifies that you'll be able to view and update any file on it, which includes crucial system files. You may also install software which can change certain settings on the server during the process, so that the installation can be done only if you are logged in as the root user. The latter 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'd like. You may also make various other users either with similar rights or with fewer rights, according to what you want them for - daily tasks, other server admins, etcetera. To be on the safe side, it is usually recommended to employ the root account only when you actually need it and not for tasks that you can do through other accounts. You may use a web-based graphical interface or a Secure Shell console to be able to connect to the server and to manage it at the root level.