Ok, It's hard to explain so I'll use an example.
1/5 + 2/15
now you try to find a number that goes into both for this example it would be 3
3*5=15 and then that equals the 2/15
so you then multiply 3 by the numerator getting the fraction
3/15 + 2/15
with the answer of
5/15 which can be reduced to
1/3
