The Camera Operator, as the name suggests, operates the camera.
They are the second-in-charge (2IC) to the Director of Photography when there is a full camera crew. This allows the DP to focus on the look of the film.
A good camera operator knows the intricacies of the specific camera. They are good at directing their team and following the DP’s orders.
The First Assistant Camera / Focus Puller reports to the Camera Operator.