You can communicate directly in Blackboard by using Messages. For detailed instructions, see Blackboard Help.
Your instructor might prefer communicating by email. If that's the case, your instructor will provide you with their contact information.
Discussions are often used to encourage discourse and engagement between students and/or the instructor, whether it's introducing yourself, discussing your goals, or exchanging thoughts about a particular topic related to the course. You can find discussions in the Discussions tab in the top menu:
You might also see discussion linked from items in the Course Content area.
Your instructor may require a level of engagement in a discussion. For example, you might be required to submit your own post before you can see your classmates' posts, or you might be required to post a certain number of replies.
In some courses, you might work in Groups within Blackboard. Your instructor will usually create the groups and assign students to them.
For more information about working in Groups, including a video, see the Blackboard Help Site.