Am I reading a chapter or a book in The Iliad (Penguin Clics)?

For summer homework I have to read the first 12 Books of the Iliad :( , I have the Penguin Clics Ver., I can't tell If I'm reading one of the 24 (I think there is 24) books or one of the 24 chapters. The first chapter/book is "Plague And Wrath". The 12th chapter/book is "Hector Storms The Wall". Are these chapters or books I'm reading? I really need to know, Thanks :D