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