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