Both the numerator and denominator are divisible by 2 so you divide it by that. you stop dividing whenever none of the numbers can be divided by the same number.
8/22 in simplest form would be 4/11 because 8 divided by 2 equals to 4 and 22 divided by 2 equals to 11 and 12/14 in simplest form is 6/7 because 12 divided by 2 equals to 6 and 14 divided by 2 equals to 7