To step into someone else's shoes is to consider their perspective before passing judgement. This is evident in several aspects of this novel. Jem resents being forced to read to Mrs. Dubose, and doesn't understand why his father insists. He thinks she is obstinate and intolerable. But, he sees a different aspect of her when he learns that she battled a morphine addiction and overcame it. He is able to realize that some of her crankiness was due to pain he was unaware of.
Scout is quick to laugh at Walter Cunningham's rude and uncouth ways, yet both Atticus and Calpurnia make her realize that Walter has had no guidance in proper etiquette or social behavior. His upbringing and poverty was beyond his control, and Scout learns to be more considerate of his feelings.
Atticus teaches his children to step into other's shoes as a way of seeing things from more than their own perspective.