There is a lock mechanism that prevents moving shifter out of PARK unless your foot is on the brake. You can bypass this by sticking a small flat blade screwdriver or a key into the little slot on the console by the shift lever.

Are your brake lights coming on when you press the brake pedal?The shift lock is released electrically when your foot is on the brake, and the sensor is tied to the brake light switch circuit. The brake light switch can be seen if you look under the dash at the brake arm. First, check the connector. If the switch is out of adjustment, you can screw it in or out to adjust. Or just buy a new one.