Traction control what is it function to the vehicle

When you have it set to on your car uses the anti locking break system to keep your tires from spinning out of control causing you to lose traction. when you have it off, it is up to you to try and keep traction.

Are you supposed to keep the traction control on or off?

Keep in on in normal driving. Turn it off when things get really slippery because it interferes with the car moving by applying the brakes too much.