Here's a couple videos:

www.youtube.com/watch?v=iG4fIor1hy4&NR=1 Cat Rocks!

www.ehow.com/video_4954595_softball-pitching-curveball-grip.html The middle finger pulls the ball towards the plate. If you were wearing a daimond ring on your middle finger, your would try to point the diamond at the catcher.

take lessons and youll learn how :)

having the proper grip and movement is important things to consider when changing your pitch

http://www.softballperformance.com/softball-pitching/the-essentials.html

There are alot of ways you just have to find the best way for you... Beware that if you teach yourself,you may do it wrong...the curve bal is a great pitch to tear your shoulder up on