As above. Thanks in advance.
It's a placeholder like any of the other sub forums: Reviews, Sessions, etc.
You are essentially playing a play by mail game through the Play by Forum portal.
The typical approach is to find some people that want to play, and then you start a thread for it in the play by forum "sub forum" and have at it. Then other people get to watch and perhaps even make comments, if you want them to.
There are no special functions to support the game in the forum, at least as far as I know. You have to figure out how to display the information for the players and track the turns yourself.
People often use VASSAL* or some other online tool to track the game state, but everyone could also just set the game up in a spare bedroom or what have you and keep the game turns updated as they are posted in the forum.
The forum can also be used to connect with players that want to play online using some other portal.
Here's an example of a rather ambitious play by forum for Earth Reborn
if you want one example of how it works.
*A tool that provides a virtual board (with all the pieces) for playing the game. It doesn't have any AI built into it, it's designed for human players. www.vassalengine.org