Atticus was simply stating that people often judge other people and only look at things through their point of view. It is as if they have tunnel vision. He thinks that the only way to really learn about someone is to think that you are them and consider how they are feeling and what things are happening to them. For example, Scout doesn’t understand Mrs. Cunningham, who is brand new and doesn’t know anyone or the culture. She is used to being around people who, evidently, aren’t farmers. If Scout puts herself in Mrs. Cunningham’s shoes, she can maybe see why Mrs. Cunningham was so ignorant about bugs and certain families.
If Scout could next look at Walter Cunningham, who she is not too crazy about, she could maybe see him in a different light. Walter made Scout “start out on the wrong foot” and he held an adult conversation with her dad that made her feel left out. However, Walter has a very poor family, so if Scout tries to see things like he does, she would realize that he spent most of his time on a farm and had to grow up very quickly to help his dad. That’s why he and Atticus had so much to talk about.
Lastly, Scout needs to realize that Boo Radley has absolutely no idea how to talk to people outside his family, or even his house. He has been mistreated and abused by being locked up since he was small, and is considered an outcast. Scout would be considered the exact same way if this were to happen to her.