If you have root-level access to a hosting server, it indicates that you will have full control over it. That is to say, you'll be able install any server-side app regardless of the changes that it will make to the software setting on the server, and you will be able to both access and modify any file, which includes system files, and modify various settings. This can be done by connecting to the server as a root user that has full privileges to perform the aforementioned things as well as to make other users, including users that also have full privileges. The connection can be established using 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 employ the root user only when you need to customize the server or to install software that may be needed by some script-driven app that you'd like to run.