Complex sentence: Quartz Compositor is the name of the component, that is fulfilling the tasks of a display server and of a window manager in the windowing system, that is being natively used by the Mac OS X family of operating systems.
Split into simpler sentences: Quartz Compositor is the name of the component that is fulfilling the tasks of a display server and of a window manager in the windowing system. It is being natively used by the Mac OS X family of operating systems.