Discrete math (macm 101 question)

i need to understand this notation:

permutation general formula : npr = n! / (n - r)! n stands for the total number of things we have, but what about r ?

is the number of objects from the total objects that you want to permute.

For example, if I have the set of characters , I can choose to permute any of up to 4 of the characters. Suppose I take just 2 of them. Then the formula predicts I should find possible permutations. Indeed, these are