If you have root-level access to a hosting server, it means that you will have full control over it. That is to say, you'll be able install any server-side application irrespective of the changes that it will make to the software environment on your server, and you're able to both access and update any file, which includes system files, and change various settings. You can do this by connecting to the server as a root user which has full privileges to do all these things as well as to generate 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 security reasons, it's recommended that you create 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 required by some script-driven app that you want to run.