How do I select a style, there doesn't seem to be an option for it.
First, I think it can be easy to confuse two related but different terms that I use when referring to the "look" of the cards.
A Layout refers to how a full page of cards prints out. There are currently two Layouts. Portrait, which means the cards themselves are in a portrait Layout like Magic cards. This Layout prints two rows of four cards per page. The other Layout is Landscape, in which the cards are turn on the side like index cards. These print out as four rows of two cards per page.
A Style refers to the actual look and formatting of a specific card on the page. This includes bold text, having the bar across the top of the card a specific color, images and where they are placed on the card and much more. There are two or three Styles currently for each Layout. The main difference between the Styles currently is how the side boxes appear (if they do). In the future I hope to get other designers to help create some more Styles to show the cards differently.
Now to answer your actual question. =)
On the right side of your screen you should see your current Print List. At the bottom of the Print List there are two selection boxes. The first selection box allows you to select the page Layout. The second box lets you select the card Style.
After pressing the Next button you should be shown a preview of the cards that you have selected. (Note: This preview only looks correct in IE because the HTML to PDF converter that I am using formats its pages the same as IE (it probably uses IE to render the pages). I personally use Chrome or Firefox, but we work with the tools that we have.)
At the top of this preview page, there is a selection box that will allow you to change the Style used for all of the cards. Or underneath the preview for each card there is a selection box that will allow you to use a different Style for that specific card. This is helpful when the text of the card is too long to fit on your normal selection. Or if you just want some cards in a different Style.
Simple answer: Just look for the selection boxes. =)