When the kids at Scout's school say racist, nasty things to Scout about Atticus defending a black man she has the courage to stand up for him. She stands up for her father not because she knows exactly what it is she is fighting for, but she believes that her father is in the right as it were. In comparison the other children are simply stating what their parents positions are on the subject because at this point in their lives the don't think in terms of right or wrong, the barley think at all, they are just absorbing the ideas around them and regurgitating them back out. Therefore Scout has the courage to stand up for something she knows little about simply because she believes in her father.
Scout, Jem, and Dill help Atticus face down a mob that wants to lynch Tom Robinson and this is showing courage. One reason is when Jem is told to return home by his father he takes his stand using his own thoughts and opinions about what is right and stays right there to face the mob with his father. Another reason is Scout has the nerve or courage at that moment in time to simply strike up conversation with one of the men in the mob. She simply asks Mr. Cunningham how Walter is doing and it snaps in back into his humanity enough to make the mob leave. After the mob departs they discover the Mr. Underwood was in the