A golf club is a third cl lever...but how does the club change the effort force needed by the golfer?

By increasing the length of the lever arm. If the golfer tried throwing or hitting the ball with his or her own hand, the lever arm applied would be about 0.5 m at best. But with the golf club, one can extend that lever arm to about 1.5 m, or about 3 times as long. So, for the same speed of arm motion, one achieves 3 times as much speed at the club face. Also, since the wrists act as an active hinge, the club face speed can be even faster. That faster speed translates into further distance for the ball.