How do you throw a curve ball??

There are 4 types of ball's motion: 1.straight(we as non-pro bowler always do this!) 2.hook(curve,just like pro bowler do in TV) 3.crank(curve,but larger angle,bowler always throw ball from beside of lane) 4.spin(helicopter,popular among Asian bowler.I am learning this technic) yes,the best way to perform curve ball is leave thumb out.if you cannot keep your palm,you need to loose your thumb...I mean,your thumb is still inside the hole..but dont grip ball with your thumb,just locate thumb in the hole... you can also perform crank by keeping your palm side perpendicular to foul your horizontal view or in other word,your two other fingers(those are not in the holes) are directly face the pins.just keep that position from your approach until your release. you may ask pro bowler to know the exact method though...