In chapter 3, Scout is dejected after a dismal day at school. After looking forward to going to school, her teacher has turned out to be less promising than Scout had hoped, and Scout has landed herself in trouble with Miss Caroline more than once in her honest efforts to help her teacher understand the Maycomb students. Scout is especially upset that her teacher has forbidden Scout's beloved reading time with Atticus.
In this quote, Atticus tells Scout that she needs to try to understand Miss Caroline's point of view and not to judge her so quickly or harshly. He explains that instead, Scout should try to understand why Miss Caroline has acted as she did and said the things she said. For example, he tells Scout that students could not expect their new teacher to understand all of the "Maycomb ways" in one day and could not hold her accountable for things she could not have known before she began teaching there.
This is a philosophy which guides Atticus in daily life. When the Cunninghams can't pay their debt for legal services, Atticus understands and allows them to pay in other ways, such as hickory nuts. When Tom Robinson's friends fill Atticus's kitchen with food following the trial, he is moved to tears, understanding what a financial sacrifice this is during the economically difficult 1930s. And even when the despicable Bob Ewell threatens him, Atticus explains that Bob has lost a great deal as a result of the trial.
This philosophy of understanding others' views in his daily interactions makes Atticus an empathetic source of guidance for his children.