The topic of the discussion is the general idea that it is focused around.
The audience is who it is aimed at, think about gender, age, race and social class. You can normally determine this by the topic and the language used.
The purpose is the reason for the discussion, is it to inform, persuade or advise.
Level of formality is basically how relaxed or polite it is, very formal would be something like a business proposal and very informal is like just talking to your best mate.
