If you want students to discuss something, open your course's discussion board and click the "create forum" button. It looks like this:
Enter a subject line and a forum description (usually a discussion prompt), but you don't *have* to specify anything else if you don't want to.
Common specifications are:
The most basic way to use the chat tool is as a real-time meeting space. It's especially good for holding office hours.
If you want to record your chats so students can watch them later, consult the instructions from Blackboard.com.
You can allow access to your webcam and/or microphone if you wish. There is a text-only chat tool, and for slower connections, it's the best choice.
Here's how to set up a chat: