I found the answer confusing and misleading.....
Modulus is what is left over IN THE FIRST NUMBER after dividing the second into it as many times as possible.
1 % 1 = 0 because after dividing 1 into 1, one time, there's nothing left
2 % 1 = 0 because after dividing 1 into 2, two times, there's nothing left
1 % 2 = 1 because 2 won't go into 1, so 1 is left