Discussion forums are available only for Type B (Facilitated) and Type C (Collaborative Workshop) courses. They are spaces where learners can share their opinions, ask questions, and connect with peers and facilitators by creating threads or comment to already created threads.
If participation in a discussion forum is essential for course completion, during the course creation, those forums should be marked as required. Contributions in required forums count towards the overall progress, only once a facilitator has reviewed and approved them.
Contributions in optional discussion forums don't count towards the overall course progress.
A discussion forum can also be used for facilitator announcements. Such forums, need to be marked "Announcement only", so that only facilitators can create threads there.
See more details on how to build discussions in a course and how learners can interact with forums in the video below.