The Forum Module provides registered users of your site a way to interact to discus topics, ask questions, and provide feedback. Lots of businesses/organizations will use a forum on their site as a form of support for their services and/or products. It allows customers/users to ask post questions and commments. The posts on the forum will remain as longs as they are not deleted, so users can also search on discussions that have already occured.
The forum has countless options. Some of those options include user rankings according to how many posts they have made, rating posts, e-mail notifications when posts or changes are made to threads, and the forum can be syndicated (RSS feed).
If your forum is viewable to all users, anyone can view all of the posts, but only registered users can make posts to the forum.