With different editions of the book in print, pages numbers can vary, but the important point is that Atticus's quote on courage occurs at the end of chapter 11, in the second to last paragraph. Here, Atticus tells Scout and Jem what true courage is:
It's when you know you're licked before you begin but you begin anyway and you see it through no matter what.
This definition of courage applies as much to Atticus as Mrs. Dubose, the woman Atticus is talking about. Atticus will show true courage by seeing the Tom Robinson trial through with honor and integrity even though he knows from the start there is no way Robinson can be found innocent of rape in the racist south.
In the context that Atticus is discussing, the difficult Mrs. Dubose, who angers the children by insulting both them and their father, has died just after kicking a morphine addiction. As a punishment for knocking the heads off her camellias, Atticus had insisted that Jem go every day and read to Mrs. Dubose. Unbeknownst to them, this has helped Mrs. Dubose stay away from morphine.
Another context is Atticus's recent shooting of Tim Johnson, a rabid dog threatening the neighborhood. Jem is impressed at Atticus's courage and his marksmanship in taking on the animal. Atticus wants Jem to understand that true courage doesn't come from shooting a gun but through living with integrity.