http://www.chess.com/forum/category/game-analysis
or
http://www.chess.com/forum/category/game-showcase
are public forums where games are posted.
In a private group, you could start a forum topic and post the game. Some groups already have ongoing forum threads dedicated to discussing games.
To post a game, you use the icon above the comment box that looks like a chess board.
If I make comments to a game from my game archive, which forum will it appear in?
Is it possible to post one of my games directly on the forum of one of my groups? IE I want to post a French Defense game diretly to the French Defense Fanatics group.
Thanks in advance.