Superlative adjectives are used to describe the highest degree of a quality and are formed by adding "-est" to one-syllable adjectives or using "most" with adjectives of more than one syllable. Examples are provided of regular adjectives like "tall," "expensive," and "beautiful" that form their superlative with "-est" and irregular ones like "good," "little," and "bad" that have unique superlative forms. The document also provides an example of using superlatives to compare people's ages.