One of the uses of Modulus is to detect if a number is even or odd.
If a number is evenly divisible by 2 leaving a remainder of zero then the number is even.
If the number is not evenly divisible by 2 and leaves a remainder of 1 then it is an odd number.
For example when dividing numbers say 8 and 2 results in a remainer of 0
So 8 is an even number.
While dividing numbers 7 and 2, results in a remainder of 1
So 7 is an odd number.
Example
Find all student ids which are even.