When you have root-level access to a hosting server, this means that you'll have full control of it. In other words, you'll be able install any server-side app regardless of the changes that it will make to the software environment on the server, and you will be able to both access and update any file, including system files, and change various settings. You can do this by connecting to the server as a root user that has full privileges to do the aforementioned things as well as to make other users, which includes 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 a separate user for your daily work and use the root user only when you have to customize the server or to install software which may be needed by some script-driven app that you'd like to run.