If you have root-level access to a hosting server, it means that you'll have full control of it. In other words, you'll be able set up any server-side app no matter what the changes that it'll make to the software environment on your server, and you're able to both access and update any kind of file, which includes system files, and modify any settings. You can do this by connecting to the server as a root user who has full privileges to perform all these things and also to make other users, which includes users that also have full privileges. This particular can be established using a web-based graphical interface or a Secure Shell console. For safety reasons, it's recommended that you create 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 want to run.