If you have a topic that is relevant for the class to discuss outside of the classroom environment, using the Discussion Boards feature is ideal. Essentially, you can choose the general areas by creating Forums, and you can enable your students to start threads of discussion, and reapply to one another's posted messages. It is basically a virtual bulletin board.

Students do not have to be logged in at the same time to communicate through the Discussion Boards. It is a wonderful place to post items such as homework questions for the benefit of the whole class, files that are to be reviewed by all fellow students, and to follow up on topics started in class when you ran out of time.
To create a Discussion Forum
To post a thread to a Discussion Forum
To reply to a posting to the Discussion Board