% is the modulus operator, mod on your calculator. It divides the number by the second and returns the remainder.
5 % 2 = 1
If you count your time in seconds and you have 5624 seconds, you can find how many minutes there are by doing floor(5624/60) and how many seconds by doing 5624%60.
It is VERY useful when calculating angle of direction, time, currency... anything that loops back to zero.