You've got to throw the ball on a downward angle.

A ball that is only moving in two dimensions (say, toward the batter and perhaps left-right) is relatively easy to hit.

Adding a third dimension to the movement (up-down) makes the hitter's mental calculations increase in complexity tremendously, and it reduces the margin for error in his swing.

There is complicated physics involved here, but just thinking it through using common sense should reveal the wisdom of pitching up-to-down.

The way to throw downward is to stay tall in the balance position and throughout the entire pitching delivery and throw, hand behind and fingers on top of the baseball.

Work on it!