I have had several people ask me how to leave comments on posts. There are a couple different ways.
If you are on the main page, just click on the comment link at the bottom of the post - it might say '1 comment' or something like that. That should pop up a comment window. Another way is if you are reading a specific post (by clicking on the post name or from the archives, something like that), and it's the only post on the page, the comment box should be listed at the bottom and you can type what you want in there.
I hope this helps those that were having trouble figuring it out (: Try to see if you can figure it out on this post, or go to another you have been wanting to comment on.