The forum is a community where you can have free discussions. These can be divided in discussion categories which can be divided in little punctual discussions.
Forums can be useful for giving support (help) for a some services or producst, because all the discussions remain posted and can be found if are searched using the intern searching system.
This platforms are easy to administrate, having an administration panel where you can add, edit, delete categories, discussions, topics or even administrate users. Also users can have different permissions, including moderator and administrator.