What does Scout do in the beginning of the book, and how does she learn from it?
In Chapter 3, Scout beats up Walter Cunningham Jr. because she feels he embarrassed her in school. Jem breaks up the fight and invites Walter to their house to eat. When Walter puts syrup all over his food, Scout makes a big deal about it and Walter is embarrassed. Cal takes her into the kitchen and scolds her:
Hush your mouth! Don’t matter who they are, anybody sets foot in this house’s yo‘ comp’ny, and don’t you let me catch you remarkin’ on their ways like you was so high and mighty! Yo‘ folks might be better’n the Cunninghams but it don’t count for nothin’ the way you’re disgracin‘ ’em—if you can’t act fit to eat at the table you can just set here and eat in the kitchen!
When Cal says Scout's folks might be "better than" the Cunninghams, she means they have a bit more money and are more educated. Cal is trying to teach Scout that she should be respectful of others regardless of their education or income levels. In the novel, this is Scout's first lesson about the differences in social class.
During Scout's first days at school, she repeatedly tries to correct Miss Caroline. In fairness, Scout is only trying to help. She tries inform Miss Caroline that Walter can not accept a handout. Miss Caroline doesn't know this nor does she know the special arrangement allowing the Ewell children to basically do whatever they want. In Chapter 3, Scout recalls a lesson Atticus taught her:
Atticus said I had learned many things today, and Miss Caroline had learned several things herself. She had learned not to hand something to a Cunningham, for one thing, but if Walter and I had put ourselves in her shoes we’d have seen it was an honest mistake on her part. We could not expect her to learn all Maycomb’s ways in one day, and we could not hold her responsible when she knew no better.
This lesson of considering the perspectives of others ("putting yourself in another's shoes") is repeated throughout the novel.