Either click on POST REPLY and enter your comment there, followed by clicking on SUBMIT REPLY.
Alternatively, scroll down past the last post and enter your comments in the QUICK REPLY window and click on POST QUICK REPLY.
After you do either one of these, you have to refresh the page (click on the REFRESH button in your browser) to see the post.
"If you want to make an apple pie from scratch, you must first create the universe." -Carl Sagan