If the key is stuck in the ignition slot... try to wiggle or turn the steering wheel with the key in the full off position. The steering column is locked and turning it while pulling out on the key should loosen it. Keep trying and turn the wheel both to the right and the left.
Be very careful or the key will break. Tap the column just under the ignition while gently turning and pulling the key. Lube the keyhole after you get it out.
Try to get the wheel to turn. Sometimes there is a steering lock that might grab the key. If that doesn't work make sure the car is fully engaged in park and that the key is in exactly the position.
First check your car for a button that releases the key. If there is no button, or you can't find one, try contacting a local dealer in your area. Worst case scenario, you'll need to call a professional locksmith.