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 NTSB says it has recovered data collectors from a jet carrying 64 people after it collided with an Army Black Hawk ...
Officials said they are still investigating the official cause of one of the nation’s worst air disasters in a generation.