What would cause my car to stall when driving it or when i brake or put it in gear?

I first would check the Mass Air Sensor ( the MAS) try tapping on it with a screwdriver handle - if the car dies then you need a MAS...also check the EGR valve to make certain it is not stuck open. Check the fuel pressure and also make certain to so have the car scanned to see if there are any Engine codes.