Having root-level access to a server means that you can view and update any file on it, which includes essential system files. You can also set up software which can change specific settings on the server throughout the, so the installation can be performed only if you're signed in as the root user. The latter has full privileges, which means that you will have full control over the machine at any time and you will be able to perform anything you'd like. You can also make additional users either with identical rights or with fewer rights, depending on what you want them for - daily tasks, other server admins, etc. To be on the safe side, it is generally recommended to use the root account only when you really need it and not for tasks that can be done through 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.