Creating a new thread is easy. Navigate to the forum you'd like to post your thread in - make sure it's the appropriate forum.

Once you've navigated to the forum, there should be a "Post New Thread" icon in the top right of the forum page that lists the threads. It's circled in red in the below image:



To post, simply click that icon. You should then go to a form where you can enter your thread. Add the title, content, and click Submit/Post and your thread will be posted.