Go to the forum main page, here http://www.tortoiseforum.org/index.php. Pick the section you think your thread pertains too, let's say "General tortoise discussion" here, http://www.tortoiseforum.org/index.php. When you click on that, to the top right you will see it says "new topic". Click that and your ready to type your thread.
Okay, I don't know why, but my links are not working. Follow the instructions and not the links.