How old are you? If your not 18, why are you are you asking this question?
To answer against my better judgement, I held mine with my index finger running parallel with the seams, so that it was in the bottom of the horse shoe. As my arm came forward, My knuckles were facing like a fastball, but instead of flipping it out like a fastball, I would snap it over to one side ( like turning a door handle). This makes the ball come out spinning like a bullet. In order to make this pitch work you MUST get TREMENDOUS rotation. If you do not, it will hang, and go pretty straight. This is a homerun pitch, because there is very little variation in speed.
If you can command your fast ball and change up, and throw your knuckle curve for strikes, you are well on the way.
Take a look at Steve's article in the summer about 3 pitches are all you need, If you need a 4th, your pitching coach (& the batters)will let you know. Ian.