Pronouns take the place of nouns and refer back to those nouns, called antecedents. Some common pronouns are I, me, my, you, he, him, she, her, it, they, them, we, and us. Pronouns help avoid repeating the same nouns over and over. The document provides examples of pronouns correctly replacing nouns like "Halloween" being replaced by "it" and "Robert" being replaced by "he". It also lists different types of pronouns and has interactive exercises for identifying the correct pronoun to use in given sentences.