The volley is the most reactive shot in the game. Because you are in front of the net, there is not time to react to the ball.
The common grip for the volley is the Continental grip. You can play these following games for learn the volley, by having a coach feeding you different shots.
When the ball lands near your feet, step in a place the racket under the ball. This is like catching the ball. Be careful though, the outgoing ball will be a floater for your opponent, so it will be easy to hit.
Here your going you block and make sure the fast ball does not hit you. A technique in returning this shot is to do a short swing and stop during contact.
When the ball is soft and high, you should raise your racket and swing down on the ball like a hammer. This is a nice put away shot.