If you have root-level access to a server, this means that you'll have full control over it. That is to say, you can set up any server-side app whatever the changes that it will make to the software environment on your server, and you'll be able to both access and customize any file, which includes system files, and modify various settings. This can be done by connecting to the server as a root user who has full privileges to perform the aforementioned things as well as to create other users, including 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 is recommended that you make a separate user for your daily work and employ the root user only when you have to customize the server or to install software that may be required by a script-driven application that you wish to run.