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