According to Atticus, what is real courage? How does this relate to Atticus defending Tom Robinson?

Atticus will defend Tom Robinson because it is the right thing to do and no amount of intimidation or pressure will stop him.

"I wanted you to see what real courage is, instead of getting the idea that courage is a man with a gun in his hand. It's when you know you're licked before you begin but you begin anyway and you see it through no matter what. You rarely win, but sometimes you do."