Tiptapp credits will give you a discount when advertising. You can add a campaign code by opening the app and use the upper left meny to find "Add campaign code".
Any credits and amount that you will pay will be shown when entering the amount you will pay for the ad.
You may get an option to share your ad on facebook in order to receive some Tiptapp credits. This can only be done directly from that screen and you wont be able to share it afterwards to get any credits.
The Tiptapp Credits will expire after a while, often after about a month