Usually the parking (hand) brake is still on. If it stays on after you release it, it can also point to low brake fluid or a brake system fault.
Can I keep driving?
Release the parking brake fully first. If the light stays on, don’t keep driving: the brakes may not be working properly.
What to do
Check the parking brake is fully released, and that the lever or button is all the way down.
If the light stays on, check the brake fluid reservoir level (under the hood, marked MIN and MAX).
If the fluid is low, or the brake pedal feels soft, don’t drive. Call for help.
If the fluid is fine but the light remains, have the brakes checked soon.
General guidance, not a diagnosis. Warning lights vary between cars, so check your owner's manual too. If you're ever unsure or the car feels wrong, stop and call for help.