If you have root-level access to a server, this means that you will have full control over it. In other words, you can install 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 customize any kind of file, which includes system files, and change any settings. This can be done by connecting to the server as a root user that has full privileges to perform the aforementioned things and also to create other users, including users that also have full privileges. The connection can be established with a web-based graphical interface or a Secure Shell console. For safety reasons, it's recommended that you create a different user for your everyday work and use the root user only when you have to modify the server or to install software which may be needed by some script-driven app that you wish to run.