A web poster will send the turn summary and save game with some additional meta information to a web server at the end of each players turn. The web server provides extended logic for dealing with the participating players.
This is different from posting to a Forum, because you are posting to a customized website that is not a forum. The website decides how to handle the game save and any other information.
Web posters require a running and configured web server, to learn more click help again after selecting a specific web poster.