Grips are trained lighting and rigging technicians. Their main responsibility is to work closely with the electrical department to put in lighting set-ups required for a shot.
The key grip is the chief grip on a set, and is the head of the set operations department. The key grip works with the director of photography to help set up the set and to achieve correct lighting and blocking.
Best Boy (Grip)
The best boy grip is chief assistant to the key grip. They are also responsible for organizing the grip truck throughout the day.
The grip in charge of operating the camera dolly is called the dolly grip. They place, level, and move the dolly track, then push and pull the dolly, and usually a camera operator and camera assistant as riders.