I ordered the Naza-M Lite from Bizmodel, an italian DJI reseller and therefore I received it few days after my order.
The main task for a flight control board is to adjust the power of the motors in order to stabilize the quadricopter, reducing the unwanted movements (oscillations, rotations…).
More advanced control boards, like the Naza ones, are also able to automatically maintain the altitude. Once the quadricopter is moved to a given altitude, you can leave the throttle: the control board will adjust the power to maintan the quadricopter at that altitude., Thanks to the GPS sensor, some control boards offers also some advanced features, like homing (in the absence of signals from the transmitter the quadricopter is returned to the point where it took off) and waypoint navigation (you can configure a path on your PC and the quadricopter will autonomously follow it).
A very good comparison table about the features of the most famous control boards is available on the OddCopter website.
Here are some photos about the unboxing of my Naza-M Lite, you can see the main board, the power board (black), the GPS module (white disc) plus some cables and holders: