This document discusses the use of apostrophes to show possession. It notes that an apostrophe plus "s" is added to the end of a noun to show that it possesses something. For example, "the girl's hat" or "Erin's jacket." It also explains that for plural nouns, only an apostrophe is added after the plural "s" to show joint possession, like "the soldiers' tank." The document provides examples and interactive exercises to reinforce these rules.