We define combinations as the ways of choosing objects from a set of an objects. In other words, order does NOT matter. We explain this concept by comparing permutations to combinationsto get from a permutation to a combination, we divide by the total number of ways to order the objects we choose. In other words, nCr = nPr / r!

I tried to include visuals to make this idea as clear as possible, and the formula is at the end.