A hook shot in golf is described as a ball that would start to the right of target for a right-handed golfer and turn dramatically from right to left, and finish away to the left hand side of the desired target. The hook shot occurs when the club face is pointing to the far left in regards to the swing path.
If the swing path is aggressively in-to-out and the face is closed to that path, then the back spin on the ball will be tilted to the left, causing the ball to move in the air from right to left. Many golfers like to see the ball move from right-to-left subtly as this would be classed as a draw if it is to finish on target.
However, a hook can be a very destructive and a troublesome bad shot. In order to promote straighter shots and reduce the amount the ball hooks, focus on the idea that your hands may be too aggressive in their releasing or flicking action which could be allowing the club head to overtake the hands before you impact the golf ball.
If this is happening it will have the effect of aggressively closing the club face, aiming it too far to the left and producing the aggressive right to left spinning hook shot.
If you can feel that the club head stays behind the hands for longer during the downswing and that the left hand takes a more leading role, therefore forcing the right hand to be more passive, they should create a slightly more open club face position through the impact phase and result in straighter longer more consistent golf shots.