Verified answer

Well at least Jimmy got part of the answer right....

When the brake light comes on, there are two possibilities.

1) you have your emergency/parking brake on

2) You have loss of pressure in the brake lines. Many things can cause that. Check the master cylinder for a lack of fluid. Fill if necessary. If NOT then stop driving that car (completely stop) and get it into a repair shop to repair the problem.

First check the brake fluid level. If it is really low top it up and have your brakes serviced as you could have a leak somewhere in the system this can be very DANGROUS. If the brake fluid is topped up it could possibly be a ABS sensor going bad or loose connection at the sensor. Another possibility the brake pads are worn and need replaced some VWs have brake wear sensors on them. In any case have your brakes looked at.