Chevrolet 2004 Express Van Owner's Manual page 96

To open the sliding door from inside, turn the handle
upward and toward the rear of the vehicle. Then, slide
the door toward the rear of the vehicle to open it.
2-12
To close the sliding door from inside, grasp the inside
handle and slide the door toward the front of the vehicle
to a closed position.
Make sure the door is completely closed before
driving away.