The function of the grip is to control the club face. The hands work as a unit to deliver the club head to the ball squarely and speedily, producing accuracy.
Most golfers use an overlapping, or Vardon, grip, with the little finger of the bottom hand placed over the forefinger of the top hand (see photo).
With nine fingers on the club, you can generate good power, but the problem with the overlapping grip is that the bottom hand is usually stronger and can overpower the other hand. A hook often develops.
Because of that tendency, some golfers use the double-overlapping grip, with the last two fingers of the bottom hand overlapping the first two fingers of the top hand. I switched from an overlapping to a double-overlapping grip in 1966, shortly before I joined the tour, to correct such a hook.
This grip forces you to swing at a slow pace, giving you greater accuracy. However, you do lose distance, and may have to adjust your overall game; you may play a club shorter.
Some golfers, such as Art Wall and Bob Rosburg, use the baseball grip, in which all fingers are placed on the club as if they were hitting a baseball. This gives you greater distance than the other two grips, but you will hook more.
I have found that many golfers grip the club too tightly. If you put too much pressure on it, you will lose control, particularly on the backswing. You should put as much pressure on the club as you would if you were holding a knife or fork at the dinner table. Next: addressing the ball