In this video, PGA Teaching Professional Todd Kolb teaches you the difference between a strong and weak golf grip. As a right handed golfer, the top hand being your left hand, a strong grip is considered seeing three or four knuckles. The right hand will be in a similar position with the V that is formed from your thumb and index finger going towards your right shoulder. Both hands will be towards the right side of the grip as you look down towards the club head. This type of grip can be used if you would like to hit a draw or turn the ball over from right to left.
Now, a weak grip will be just the opposite. As you look down at the golf club, the right hand will show about one knuckle. The V that is formed again with your thumb and index finger will be pointed more towards your chin. This is also true with the right hand where you will see it more on top of the golf club and the V is pointed towards your chin instead of your right shoulder. This can be used to try to hit a fade golf shot or from keeping the ball from going right to left.