There are three pressure points we need to establish in the hands during the golf swing.

Pressure point No 1:
The last three fingers of the top hand

Pressure point No 2:
The Lifeline of the bottom hand against the thumb of the top hand.

Pressure point No 3:
The first knuckle of the bottom hand index finger against the side of the handle.

Pic from The Golfing Machine

A problem I encounter sometimes with students is when they lose connection of the second pressure point and therefore lose the structure of the arms at the top of the swing.

I could go on for hours..

However, this video I think would explain it a little better..