Adding and subtracting fractions is a simple process that involves finding a common denominator. The document explains that a fraction has a numerator and denominator, and the denominator represents the whole or size. It provides an example of adding 1/4 and 2/3 by first multiplying the fractions to have a common denominator of 12, then simply adding the numerators to get the sum of 11/12. The document emphasizes that finding a common denominator is key to easily adding and subtracting fractions.