Well you look like you figured out how to post a thread. You can get a lot of information here (bottom right on every page): http://onlinetradersforum.com/help/ Most of it though is common sense. Look right after a thread and it says "Write your reply..."
Make sure you are facing the computer monitor, then click on the button that is in the top right and says "post new thread"
Just being logged in isn't enough. The "Post New Thread" button doesn't appear on the home page. Click on a forum section. The first section is "Stock Picks And Trading Strategies". Once you're in a section, then you should see the "Post New Thread" button.