The program is called DubLi, and the link above takes you to a video which explains how it works. It's pretty easy! Just search, shop, and get cash back. There are really quite a lot of well-known stores which participate. In addition to shopping at websites like Target and Macy's, you can also get travel deals on sites like Hotwire and Priceline. You'll find exclusive deals and coupons, too.
Personally, I've used discount programs in the past and enjoyed them, but I've never tried one with a toolbar before, and the simplicity of using this type of shopping portal seems like it would be worth a try.