On the interior of a car door, the door-lock actuator is the mechanism that controls the door lock. The actuator is located directly below the key latch. A thin metal rod goes between the actuator and the key latch and connects the two.
A second thin metal rod connects the key latch to the knob that sticks out of the top of the inside of the door (the knob that goes up and down to indicate whether or not the door is locked).
When the actuator is in operation, it moves the door locking latch either up or down (either via a supply of power for power door locks, or manual force from manual locks). When the latch is in the "unlocked" position, the door handle on the outside of the car is directly connected to the opening mechanism. This allows the door to be opened and closed at will. When the door locking latch is in the "locked" position, the door handle on the outside of the car is disconnected from the opening mechanism, which disables a person on the outside of the car to open and close the door without a key.
