The key is stuck in the ignition and the ignition cylinder will not turn.
If it is an automatic then you need to turn the car on and put it in gear and then back in park and see if that frees up the switch. Also turn the steering wheel to the left while holding the brake down may free up the key. If these things do not work you may need to have the ignition switch replaced by a technician from YourMechanic. It will require removing part of the steering column.