Through Greg's diary, the exposition details his daily struggles, such as avoiding the school bullies, trying to impress his crush, and dealing with his annoying family members. It also introduces some of the other main characters, including Rowley Jefferson, Greg's best friend; Mr. Jefferson, Rowley's father, who is also Greg's school principal; and Fregley, a strange and eccentric classmate.
The exposition is essential to provide the context for the subsequent events of the story, allowing the reader to become familiar with Greg and his world.