When you have root-level access to a server, this means that you'll have full control over it. That is to say, you can install any server-side app irrespective of the changes that it will make to the software environment on your server, and you'll be able to both access and change any file, which includes system files, and modify any settings. This can be done by connecting to the server as a root user who has full privileges to do all these things as well as to create other users, which includes users who also have full privileges. This particular can be established using 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 employ the root user only when you have to modify the server or to install software which may be required by some script-driven app that you wish to run.