Only after you've logged in will you see the buttons to "Reply to Thread". It should be at the top and bottom of every thread page, and a "reply with quote" button under every individual post.
Also, when in a post, you can go to the bottom white area, type something up there, and click "Post Quick Reply"
You show all the signs of an older gentleman, so I hope when we get you educated on how to use tnet, you'll educate us on a few things with stories and wisdom. Waiting patiently!