It depends on how far you've gotten into the book as to what you know about the narrator of the story. The narrator of the story is Jean Louise "Scout" Finch as an adult, looking back upon events that happened when she was between 6 and 8 years old.
Right away at the beginning of the story, we find out that Scout has a brother named Jem who is 4 years older than her, and that he broke his arm when he was 12. We know she has a father named Atticus.
We also learn a great deal of background about how the Finch family came to settle in Alabama at Finch's Landing, as well as how Atticus and his brother Jack left Finch's Landing, leaving their only sister Alexandra and her husband to look over Finch's Landing. Jack became a doctor and Atticus became a lawyer.
Scout lives in a small town called Maycomb with her brother, father and family cook/nanny, Calpurnia. Scout's mother died of a heart attack before Scout could really get to know her. Jem remembers their mother, though.