If you have root-level access to a server, this means that you'll have full control of it. In other words, you can set up any server-side app irrespective of the changes that it'll make to the software environment on your server, and you're able to both access and change any file, including system files, and change various settings. You can do this by connecting to the server as a root user that has full privileges to perform all these things and to generate other users, which includes users that also have full privileges. This particular can be established with a web-based graphical interface or a Secure Shell console. For security reasons, it is recommended that you create a different user for your daily work and use the root user only when you have to modify the server or to install software which may be required by a script-driven application that you wish to run.