Adding a demo of how the ad unit looks was on the to-do list. I guess both of us just forgot about it before launching. We'll redo the front page with better wording and I'll add a demo of the ad unit in there.

In the future you will be able to choose the ads you want to display based on keywords and categories. Right now though, we wanted to make it as simple as possible (with the least amount of steps to get it set up) so it's automatic.