Drag your desired stacks into the top drop area. This will be used to create your launcher for the lightbox. You should be able to put whatever you want in here. However, keep in mind that links within it will probably not work.
a. If you do not want a launcher at all, simply leave this empty. This would be good if you launch from an external link and/or open Exposé on page load.
Then you can drag your desired stacks into the bottom drop area. This will be used to create your Lightbox content. This area can really contain anything that you want.
Now preview and enjoy! For an overview of the remaining settings please refer to the Expose Settings section.