If you have root-level access to a hosting server, this means that you'll have full control of it. In other words, you can install any server-side application regardless of the changes that it'll make to the software setting on your server, and you can both access and update any kind of file, including system files, and modify various settings. You can do this by connecting to the server as a root user who has full privileges to do all these things and to generate other users, including users who 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 one more user for your daily work and employ the root user only when you need to customize the server or to set up software which may be required by some script-driven app that you wish to run.