Ground controllers manage airplanes from push-back and engine start until the airplane is handed off to the next controlling agency for takeoff.
Local control primarily manages departures at a local airport. This includes active runway management.
Clearance delivery handles administrative management regarding flight information such as tail number identification, movement times and validation of departure/en route/flight termination planning.
Approach control manages processes oriented to the landing of aircraft. This control agency takes over from en route controllers.
En route controllers communicate with an aircraft during the middle parts of a flight. This process provides constant monitoring regarding any route changes, weather updates, emergency needs or other important information.