It's an app that (I believe) is only available to access if you log in via Facebook. I got signed up for on my laptop first and played around there first because I find it easier to read. Then I downloaded the app to my phone. I LOVE it.
Basically, it's additional savings of varying amounts, on top of the 5% you get with your red card. You can browse by catagories and then you put items you may want or need in your cart and then the cashier will scan the app when you check out.
At first, you are only allowed 11 (I think) items in your cart (and you can buy up to 5 of those items with the discount applied). But, the more you shop, the more cart space you earn.
For example, Market Pantry milk is in my cart and is 5% off (then I get another 5% with my red card). I always try to remember to check the app or on my computer before I head to target to compare with my shopping list to add or remove things from my cart that I may or may not need.
Today, I noticed that they had cute scarves that offered an additional 25% of, so I put those in my cart. I ended up getting 3 of them for DDs dance teacher for Christmas gifts. They were $14.99/each and so with the app and my card, I got 30% off each scarf!
Also today, large bags of Mars Halloween candy were another 10% wit the app. I noticed at the store that if you bought two, you also got a $5 gift card. So I bought two bags at $9.99/each and saved 15% and got a gift card.
It takes some work, but once you get used to remembering to look at the app before you go to the store, it's worth it!