to reduce, you have to find the greatest common factor of both numbers. The greatest common factor is the biggest number that can divide into both numbers.
factors of 8: 1,2,4,8
factors of 4: 1,2,4
the biggest/greatest factor they have in common is 4.
once u find that, divide both numbers by the greatest common factor
8/4 4
------- = ---------
4/4 1
the answer is 4.
anything divided by 1 is the numerator (number on top of the fraction bar)