This happens in Chapter 3. This is the part in the book where Atticus gives Scout the famous advice about getting in to someone's skin before you judge them. What he says exactly is
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 it.
What Atticus is saying here is that you can get along with people better if you try to understand what it is like to be them. You should not just impose your own point of view on them. You need to see things the way they see them.
If you can do that, you'll get along better with other people because you will be able to understand why they act the way they do.
This is one of the key bits of advice Scout receives from her father in Harper Lee's novel, To Kill a Mockingbird. Scout has had a particularly rough first day at school. Her inexperienced new teacher, Miss Caroline, has accused Atticus of being a poor teacher; she has gotten into a fight with Walter Cunningham Jr.; she draws the ire of Calpurnia at lunch; and then she gets her hand paddled by the teacher in the afternoon. When Scout tells Atticus that she does not want to return to school, he tells her that
"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 it."
Atticus tells Scout that she has "learned many things today." He makes a bargain with his daughter: If she will agree to go back to school, they will continue to read together each night (against Miss Caroline's wishes--and without her knowledge).
In Harper Lee's To Kill a Mockingbird in Chapter 1 on the evening of the first day of school, Scout mentions to Atticus that if she keeps going to school, "we can't ever read any more...." In response to this statement, Atticus asks Scout if she knows what a compromise is, and suggests that they compromise by mutually agreeing to read every night "just as we always have." But, as Scout goes out the front screen door, her father suggests that she not say anything at school about their agreement. In other words, what Miss Caroline does not know will not hurt her.
This lesson of reticence in the appropriate situation is certainly one that a good lawyer knows. As a loving and tolerant man and father as well as a competent lawyer, Atticus Finch imparts many such lessons to his daughter.