When you click on the icon, a widget appears where you can send the link in an email, or your can post it to various sites.
I found a problem in the way that it detects individual articles. The posts that I have that were submitted directly from del.icio.us, are not marked with the madKast icon. All of these posts have a title similar to "links for 2007-07-29". I send an email to madKast support about this problem.