Click on 'comments' at the bottom of a post.
Write your comment.
Choose an identity. If you already have a Google Account, tick the first circle. If you don't tick 'Name' and write your name. If this doesn't work for you, tick 'Anonymous'.
Now finish by clicking 'Publish your comment'. Your comment won't appear straight away as it needs to be verified by the blog owner first.
Right, now it's your turn ... looking forward to your comments.