If you have root-level access to a hosting server, it means that you'll have full control of it. That is to say, you can install any server-side application regardless of the changes that it will make to the software environment on your server, and you will be able to both access and modify any kind of file, which includes system files, and change various settings. You can do this by connecting to the server as a root user who has full privileges to do all these things as well as to generate other users, including users that also have full privileges. This connection can be established through a web-based graphical interface or a Secure Shell console. For security reasons, it is recommended that you make a separate user for your daily work and employ the root user only when you have to modify the server or to install software which may be needed by some script-driven application that you want to run.