Having root-level access to a server signifies that you can view and modify any file on it, including important system files. You may also install software which can change specific settings on your server during the process, so the installation can be done only if you're signed in as the root user. The aforementioned has full privileges, which means that you will have full control over the machine at any time and you'll be able to perform anything you need. You can also make additional users either with the same rights or with fewer rights, according to what you need them for - day-to-day tasks, other server administrators, etcetera. To be on the safe side, it's usually recommended to employ the root account only when you actually need it and not for tasks you can do via other accounts. You can use a web-based graphical interface or a Secure Shell console in order to connect with the server and to control it at the root level.