Having root-level access to your server means that you'll be able to view and modify any file on it, which includes crucial system files. You can also set up software which can update certain settings on your server during the process, so the installation is possible only if you are logged in as the root user. The aforementioned has full privileges, which means that you will have full control over your machine at any time and you will be able to do anything you would like. You may also create other users either with similar rights or with fewer rights, based on what you need them for - daily tasks, other server admins, etc. 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 that you can do via other accounts. You can use a web-based graphical interface or a Secure Shell console to be able to connect to the server and to control it at the root level.