Why does the car squeal or squeak when moving?

Two "most likely" reasons that are most likely.

A small piece of dirt or sand trapped between the pad and rotor often causes high pitched noise such as squeaks or squealing, sometimes a harsh bang on the brake pedal when driving may either loosen or melt the dirt and relieve your noise.

Make VERY sure you are able to do this in a safe area at safe speeds.

The second reason could be related to brake pads that are worn down to the wear sensor, the thin piece of metal that is designed to create that annoying noise when they rub on the rotor.

Both these two items MAY vary or go away when you either release or apply the brake

Pads that are metal on metal usually generate a grinding noise on brake apply not simply a squeal.