Scout approaches this mob that has surrounded Atticus and she thinks she's going in to socialize with all of these men, she indeed does socialize with all of these men. What she fails to realize is that they were there to torment or hurt Tom Robinson. Atticus was ready to stand in between the mob and Tom Robinson and could have likely been hurt in the process.
When the children arrived and refused to leave, Scout spoke enough about Walter Cunningham's son and entailments that the man grew an ounce of humanity in the moment and determined that he could not do something that wrong in front of a child. Scout has no concept that her innocence just saved the day.
This is the scene where the mob is at the jail, wanting to lynch Tom Robinson. The episode relies on Scout failing to understand it because she actually clears up the tension by acting in a way that is not really appropriate. If she had understood, she would not have acted that way.
Scout does not understand what the men are trying to do. So when she sees Mr. Cunningham, she engages him in small talk, just as she has been taught to do. It's not really the time for that, but it works because it makes Cunningham start to actually think about what he is doing. This makes him rethink and he helps to break up the mob.
BTW -- it is Chapter 15.