Having root-level access to a server signifies that you can view and change any file on it, including crucial system files. You can also install software that can update certain settings on the server during the process, so the installation is possible only if you're signed in as the root user. The aforementioned has full privileges, which means that you'll have full control over your machine at any time and you'll be able to do anything you'd like. You can also create other users either with identical rights or with fewer rights, depending on what you need them for - everyday tasks, other server admins, 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 that you can do via 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 control it at the root level.