Having root-level access to a server signifies that you'll be able to view and modify any file on it, which includes crucial system files. You may also set up software which can change particular settings on your server during the process, so the installation can be performed only if you're signed in as the root user. The aforementioned has full privileges, i.e. you will have full control over the machine at any time and you will be able to do anything you would like. You can also generate various other users either with identical rights or with fewer rights, according to what you want them for - daily tasks, other server administrators, etc. 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 which can be done 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.