How do you add fractions and the way to solve it involves decision because that's the way my teacher taught me but i've forgotten

To add any given fraction you must have a common denominator!
(Remember that the top is the numerator, and the bottom is the denominator!)
So, if you have an expression like this: 

1/2 + 2/3 = ? 

You need to find what is the smallest number that both 2 and 3 have in common. In this case it is 6. (Because 2*3 = 6, and 3*2 = 6)

(1/2)*(3/3) + (2/3)*(2/2)

Multiply across. (So the numerators multiply, and then the denominators multiply)

3/6 + 4/6 = ? 

Add the numerators together!

7/6, is our answer!