Having root-level access to your server means that you can view and change any file on it, which includes essential system files. You can also set up software that can change particular settings on the server throughout the, so the installation can be done only if you are logged in as the root user. The latter has full privileges, i.e. you will have full control over the machine whenever you want and you'll be able to perform anything you need. You can also make various other users either with identical rights or with fewer rights, according to what you want them for - everyday tasks, other server admins, etc. To be on the safe side, it is usually recommended to employ the root account only when you actually need it and not for tasks that can be done using 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 manage it at the root level.