4 -seam fastball is the primary pitch (two fingers across the seams, thumb on bottom)
2-seam fastball uses the same arm motion and speed, but with a different grip (with the seams)
4-seam and 2-seam fastballs
The change-up uses the same arm motion of the fastball but the grip is with more fingers causing additional friction on the ball. Young kids often use the claw grip. Older kids tend to use a circle change.
Short video instruction talking about the basics of throwing a knuckleball.