To add or subtract fractions, find a common denominator and then simply add or subtract the numerators, keeping the same denominator. For example, to add 3/4 and 2/4, find the common denominator of 4, so 3/4 + 2/4 = 5/4. And to subtract 5/8 - 3/8, the common denominator is 8, so the subtraction is 5/8 - 3/8 = 2/8.