It's very normal for brake pads to begin squealing when the brake pads wear down to an unsafe level and need replaced.
Brake pads have a little piece of metal on them that makes contact with the rotor and is supposed to make a scraping or squealing sound when the brake pads surface wears down.
If you're noticing a scraping or squealing sound when you press down on the brake pedal to stop the vehicle then it's most likely the wear indicator on the brake pads causing the scraping or squealing noise.
However if the brake pads are squealing or scraping when you're just driving down the road and not depressing the brake pedal then that could indicate some other problem with the brakes which should be checked out just to be safe.