We truly cannot understand someone until we walk in their shoes. At the end of the novel, Scout is able to do just this by walking Boo back home. She also understands more about Boo than ever before -- the unknown has become the known. Boo's reputation was mainly established by town gossip and as human beings, we are ever interested in this form of "entertainment". However, once the truth is known, it can be much less entertaining and Scout realizes that Boo is a lonely guy with no friends. Scout's innate kindness (inherited by her father) shows when she displays compassion regarding Boo's "otherness" in a town where anyone who is not "normal" is regarded as strange.
At the end of the novel, after walking Arthur "Boo" Radley home, Scout looks out at the view of town from the Radley's front porch. She notices just how much Boo could see just by looking out the window, since, being a recluse, was his only means of experiencing the world.
She also notices just how clear the view of her house was, as well as the tree. Recalling all the times she, Jem, and dill spent playing in plain view of the house, she realizes that in a sense, they were "Boo's kids", and he was actively a part of their lives, if only from the outside looking in.
It's really a touching/moving part of the novel, as it directly follows a much-anticipated meeting of Scout and Boo for the first time. He saved she and Jem from certain death at the hands of Bob Ewell, even killing the attacker in order to ensure the children's safety. Scout has a new understanding of her friend and guardian, and learns a great deal about how others can be an active part of our lives, if even unknowingly.