If you have root-level access to a hosting server, this means that you will have full control of it. In other words, you can install any server-side app no matter what the changes that it will make to the software environment on the server, and you'll be able to both access and change any kind of file, including 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 the aforementioned things and also to generate other users, including users that also have full privileges. The connection can be established through a web-based graphical interface or a Secure Shell console. For security reasons, it's recommended that you create another user for your everyday work and employ the root user only when you need to modify the server or to install software that may be needed by some script-driven app that you'd like to run.