I understand how to do the normal permutations that are like

9!/(9-4)!

9x8x7x6x5!/5!

5!'s cancel, 9x8x7x6=3024 combinations, yeah yeah yeah....but I don't understand this other permutation thing for the life of me.

What's canceling, what's doing what? They don't explain, give explicit solution, thus how am I supposed to learn? The book doesn't even give explicit solution. Math always does this to me...anyways...: