Jem and Scout go to church with Calpurnia because Atticus is out of town. Calpurnia's church is called First Purchase African M.E. Church. Scout asks Calpurnia about the hymn books. Calpurnia tells her that they do not have any. At Scout and Jem's church, the congregation reads the lyrics to the songs from hymn books.
Zeebo, Calpurnia's son, is the music superintendent at First Purchase. It is his job to lead the congregation in song. He stands up and is "carrying a battered hymn-book" (To Kill a Mockingbird, Chapter 12). He turns to face the congregation. Then Zeebo recites the words from the hymn book and the congregants repeat them in song.
Scout and Jem are amazed at this new and unfamiliar way of singing church songs. Though there are no hymn books, the congregation knows the words to the songs with the help of Zeebo.