The document discusses the use of possessive 's. It notes that: 1) We normally use -'s for people to indicate possession, such as "Ann's camera" or "the manager's office." 2) You can use -'s without a noun after it, like "Mary's hair is longer than Ann's." 3) For plural nouns ending in s, like "friends," the possessive is formed by adding only an apostrophe, like "my friends' house."