Thom, Welcome to
RTP!
If you are reading a thread in one of the forums, the POST REPLY button is at the bottom of the last reply, or you can just type in the "Quick Reply" message box at the end of the thread.
To post a new thread. Go to the Forum that best suits your subject, then at the top gray bar of the forum you will see a pop up box that says "Thread Tools". In there you will find an option to post a new topic.
For best responses, make sure you are in the best Forum area to match the subject of your post. For example, I don't read in the photography area because it doesn't interest me. But if you have a photography question, that's where the "pros" hang out.