OK, well, here's a page with a diagram of the different spaces:
http://www.w3schools.com/css/css_boxmodel.asp . That site's good in general for simple html/CSS/JS stuff. Also, if you use the FireFox browser and an add-on like DOM Inspector or Firebug you can right-click on something on your page and see the html for it, along with the CSS that was used in formatting it (That's probably the answer to your question in the other thread, about how LifesGreatestGift knew about the fb_edge_widget_with_comment class).
If you post a link to your site we might be able to help you more.