My left back passenger door lock will not lock or unlock on my 2010 Ford F-150

It sounds like to me the door lock actuator has failed. You will need to purchase a new actuator and then remove the inner door panel to access and replace. It is a bear and a tight space.

Before purchasing the actuator, remove it from the vehicle. You will have to drill out three rivets, if memory serves. It's a 12V DC motor. So you can check it by jumping it off the battery. Reversing the polarity will make it run in reverse.