The core Forum module lets you create threaded discussion boards, called forums, on your site. Forums are very useful because they allow community members to discuss topics with one another, and the discussions are archived for future reference.
Topics, or threaded discussions, are posted into a forum. Each topic is comprised of an initial post, which is a Drupal node, and replies, which are Drupal comments. Forum topics have their own URLs.
Multiple forums are often set up for different areas of discussion. Forums can also be placed inside other forums for a discussion area that is a subset of the parent forum, in which case they are often called child boards or child forums.
Containers can also be created to hold a group of forums. However, unlike in parent forums, topics cannot be posted directly into containers. Both containers and forums can be placed inside other containers and forums. By planning the structure of your containers and forums well, you make it easier for users to find a discussion area of interest to them.
The Drupal 8 Forum module requires the modules Node, History, Taxonomy, Comment and Options. They are automatically enabled if you install the Forum module.