When you have root-level access to a server, it means that you'll have full control of it. In other words, you can install any server-side application whatever the changes that it will make to the software setting on your server, and you will be able to both access and change 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 the aforementioned things as well as to make other users, including users that also have full privileges. This particular can be established through a web-based graphical interface or a Secure Shell console. For security reasons, it's recommended that you make one more user for your everyday work and use the root user only when you have to customize the server or to install software which may be needed by a script-driven app that you wish to run.