Facebook comments box

hi.
i have a website running on php.
i want to add the facebook comments box.
I want it have it for every article on my site so that every article will have its own set of comments.
can someone explain me how to do this.

Comments - Facebook Developers
or
iframe

thanks for it.
i have already started using it on my webpages.
but now i want to know the total number of comments for a particular article.
how to do that.