When you have root-level access to a hosting server, it means that you'll have full control of it. That is to say, you can install any server-side application no matter what the changes that it'll make to the software setting on your server, and you can both access and modify any file, which includes system files, and modify any settings. This can be done by connecting to the server as a root user who has full privileges to do all these things as well as to create other users, which includes users that also have full privileges. This particular can be established through a web-based graphical interface or a Secure Shell console. For safety reasons, it's recommended that you make another user for your everyday work and use the root user only when you have to modify the server or to set up software that may be required by a script-driven app that you'd like to run.