The polarizer filter idea is the same as your sun glasses, I don't want to get into scientific details about light waves, polarization and stuff, but if you're interested, you'll find a good explanation here. Suffice to say, a polarizing filter cancels a part of the light reflected from any object, be it the sky, a car's windshield or the water's surface.
So how can this be of benefit for you? I'll give you a small exercise, go outside in the morning and try shooting your car from outside and see the car's interior through the glass, mostly (depending on your angle) you'll find that the glass reflects the sky and the surroundings. Check this example: