If you have root-level access to a server, this means that you will have full control over it. That is to say, you'll be able install any server-side application no matter what the changes that it'll make to the software environment on your server, and you are able to both access and modify any file, including system files, and change various settings. You can do this by connecting to the server as a root user who has full privileges to perform all these things and also to generate other users, including users that also have full privileges. This particular can be established using a web-based graphical interface or a Secure Shell console. For safety reasons, it is recommended that you create another user for your everyday work and employ the root user only when you have to modify the server or to install software that may be needed by a script-driven app that you would like to run.