All the skin really is a bunch of Cascading Style Sheets. So all u gotta do is download the file that contains them all, change them and post them on the site.
Currently there are a bunch of style sheets for the site because we wanted to have seperate one's to make it easier to update. They might not be the most formatted or name friendly, but it works
As we continue building out the site with the new system, the CSS stuff will be revamped and simplified.
Other than that, u really need to know something about CSS in order to understand it. Soon to come as well will be a document outlining what each style is and a few images that will point out which styles are what.
Hope this helps any.