What does Calpurnia do and who is she?
Calpurina is introduced as the Finches' cook; however, later the reader realizes the parental relationship between Cal and the children. Because she is a mother like figure she has a say so in Scout and Jem's life and welfare. She also teaches (through her actions and Atticus' respect) the Finch children that skin color does not matter. Scout witness the difference between black and white in Chapter 16 when Atticus and Aunt Alexandra disagree about speaking openly in front of the "colored" help.
Calpurnia is the Finch family's African-American housekeeper and Nanny. She and Atticus, the father of Jem and Scout, have had almost equal hands in raising the two children (their mother had died four years ago). Calpurnia, with her strong religious beliefs and firm discipline, balances Atticus's relative softness and more flexible boundaries.