ABS is a reactionary system that works off hub sensors, and a deceleration sensor that tells the system when to kick in.
Once you slam on the brakes and the ABS takes over you will probably notice that your brake pedal pulses rapidly. This is a sign that the system is distributing levels of brake pressue to the wheels that will give maximum braking without letting the wheels skid....much.
on older systems, or where your suspension and shocks arent up to spec there will be a few little chirps maybe, but these are quickly counteracted as the system sees a wheel is stationary while the car is still moving and eases braking in the corner slightly.
There are many tech articles out there and search is your friend, but this info just off the top of my head should be enough to get you started.