Having root-level access to your server means that you'll be able to view and change any file on it, which includes essential system files. You can also install software which can update specific settings on the server during the process, so that 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 would like. You can also make various other users either with similar rights or with fewer rights, depending on what you want them for - day-to-day tasks, other server admins, etcetera. To be on the safe side, it's generally recommended to use the root account only when you really need it and not for tasks that you can do using other accounts. You can use a web-based graphical interface or a Secure Shell console to be able to connect with the server and to control it at the root level.