Flight Data Recorders Not Recovered Yet

What is a black box, what can it tell us, and have the data recorders been found from Flight 5342 and the Army's Blackhawk?
The black boxes are the nickname for the flight data recorder and cockpit voice recorder that record events during a flight.
The NTSB says it has recovered data collectors from a jet carrying 64 people after it collided with an Army Black Hawk ...
At least 28 bodies have been recovered after an American Airlines jet carrying 60 passengers and four crew members collided ...