I am assuming you mean Ratio into Fraction.
It is really simple, actually. Just put one number on top of another (divide would be a better word).
I have a ratio A:B, which is 1:2.
I can put 1 on top of 2 to create the fraction 1/2 to say that A is 1/2 of B.
A=1/2B
I can also put 2 on top of 1 to create the fraction 2/1 to say that B is 2/1 of A, or 2 times of A.
B=2A
