In online courses nearly all communication is written. This requires that you pay special attention to how you "say" things, since other learners do not have the benefit of picking up on non-verbal queues. Written communication normally takes place asynchronously by taking the form of posts and responses to a discussion forum. In this type of discussion, the instructor will post a topic and require students to post a discussion, respond and perhaps critique and evaluate their peers submission. Asynchronous discussion may be used to generate discussion solely among students.
There may also be synchronous discussions which are similar to chat rooms. The instructor will schedule a virtual meeting, in which students login to blackboard at the scheduled time and discuss course topics.
Read more on Netiquette at www.albion.com/netiquette/corerules.html.