True, now that I re-read his post, I see it. xD
Anyway, the link certainly helps, but to provide a bit more of focused advice: to create a game, you enter the Games tab in the upper header of the site, and then hit the Create New Game button, which is somewhere on the upper right corner of the screen. That will lead you to a form for filling the name of the game, the system, and the description. After that, the game forum will be automatically created.
To create an advertisement thread, from the game forum you must hit the "Game Profile" page, and on the upper header there will be a few options, one of them "Create Advertisement" or something of the sort. It will lead you to a form where you will put in the name of the thread, the number of players you want, the closing date (if you want one) and the thread proper. The description of the game will automatically be included in the ad as well.