(I have edited your query, since eNotes allows only one question per post.)
The text of To Kill a Mockingbird is very much Scout's story. She is the narrator and main character, and most of the events revolve around her and are told well in the future from her adult perspective. Scout undergoes many changes during the two-plus years that encompass the novel, and the lessons she learns--through her own experiences and from the people around her--reveal her developing maturity and a loss of innocence that comes much earlier than most children her age. She learns about the importance of being tolerant toward others by Atticus's words of wisdom: how
"You never really understand a person until you consider things from his point of view--until you climb into his skin and walk around in in." (Chapter 3)
From Atticus she relates the symbolic innocence of the mockingbird to both Tom Robinson and Boo Radley; and through Atticus's actions, she discovers the meaning of humility, honor and the epitome of a true Southern gentleman. From others around her, Scout witnesses racial bigotry (Bob Ewell); hypocrisy (her teachers and the women of the Missionary Circle); bad parenting (Bob Ewell and Dill's parents); and how the words of adults don't always ring true (Miss Stephanie). She discovers how first impressions are not always accurate, recognizing for herself that both Tom Robinson and Boo Radley could not have committed the crimes for which they were accused.