"I am at a loss to understand how this Board works. I've tried to reply to the topic 'Our Military Here' which momentarily appeared under Nash's original post. However, my reply was not registered on the main page and when I went back into the post the reply had disappeared!"

It sounds to me like you made a post then hit the back button to get to the main page. When you hit the back button you will see the site at the time you were there earlier. If you want to see any new posts, including yours, if you do that you need to hit the refresh button. You can also just click on the link at the top of the page after you make a post for cblf.

"PS Do you have to insert your nickname and password every time you post a reply?"

Yes