What characters say out loud — their dialogue — can serve a range of purposes. You can show a character's background and education by the words she chooses and how she puts them together. You can show the disconnect between what your character means and what she says, and between what she reveals and what she is trying to keep hidden. You can use dialogue to show how characters relate to one another. Dialogue, used well, enables you to show the reader who your characters are while moving your story forward.