There are a few examples of understanding in the book. Unfortunately, there isn't more understanding. For example, after the trial of Tom Robinson, the majority of people are still as racist as ever. That said, there are a few places where understanding takes place.
First, Scout is better able to understand people. For example, when Walter Cunningham comes to her house for a meal, Scout is critical of his eating habits. Later on, she realizes that not all people are well off. She grows in understanding people's social backgrounds.
Most notably, Jem and Scout grow in their understanding of Boo Radley as the book progresses. At first they are preoccupied with Boo. They want him to come out of his house; they mock him and fear him at the same time. As the book progresses, they begin to see that Boo is a person, a kind person at that. Later Scout understands that perhaps Boo does not come out of his house because he does not want to. Moreover, at the end of the book, Scout sees Boo as a mockingbird figure who only does good. Hence, he must be protected.
The characters in the novel who understand the most are the children.