If you have root-level access to a server, this means that you'll have full control of it. That is to say, you'll be able set up any server-side application irrespective of the changes that it'll make to the software setting on your server, and you'll be able to both access and change any kind of file, including system files, and modify various settings. You can do this by connecting to the server as a root user who has full privileges to perform all these things as well as to make other users, which includes users who also have full privileges. This connection can be established with a web-based graphical interface or a Secure Shell console. For security reasons, it's recommended that you create a different user for your everyday work and use the root user only when you need to customize the server or to set up software which may be needed by a script-driven application that you would like to run.