Yeswant, I have replied to your PM on this question but to save others the trouble of duplicating answers, here is my response:
The gyro outputs a voltage proportional to yaw rate (rate of rotation), with mid voltage (around 2.5 volts indicating no rotation. So as analogRead values increasing above 512 indicate increasing rotation rates in one direction, and values decreasing below 512 indicate increasing rates in the other direction.
This output is usually fed into a Kalman filter to smooth the data and reduce drift by combining information from the gyro with the accelerometers.
There is a lot of information on how to do this in this thread and other sites linked.
Have fun!