If you have root-level access to a hosting server, it means that you'll have full control of it. That is to say, you'll be able install any server-side application irrespective of the changes that it'll make to the software setting on the server, and you will be able to both access and customize any kind of file, including system files, and change any settings. This can be done by connecting to the server as a root user which has full privileges to perform all these things and also to create other users, including users that 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 create another user for your everyday work and employ the root user only when you need to customize the server or to install software which may be required by some script-driven application that you want to run.