Best described as a torrent of children running around in a minefield, some armed with weapons (moderators), forums are the flagship of internet discussion, spam, and flame wars.
Smaller forums tend to be more habitable, the larger ones have distinct features. For example, within approximately seven seconds of the creation of a topic, you will have at least one reply, guaranteed. Large forums also tend to spawn makeshift caste systems within themselves, and you're automatically a malefactor until you have a 4-digit post count.
A forum can sometimes be helpful, but normally they become a time consuming and frustrating thing if you pay too much attention to them.