What is module

Answer 1

What is... questions are good candidates for a google search.

Answer 2

I assume you meant modulo or modulus. This operator (usually written with a %) calculates what's left after an integer division:
9/3=3 -> nothing left
10/3=3 and 1 left
so 9%3=0
and 10%3=1
also 12%4=0
and 15%4=3