From the website:
Bonus 1,000 Yums* when you first book on TheFork app with the code APP20.
*equivalent to $20 off your next booking. Offer valid when you input the code APP20 when you first book on the app. The code APP20 is valid only once. Your 1,000 Yums will be credited to your loyalty space 7 days after the date of your meal ** Please refer to the restaurant page for the specific conditions of the offer.
Each booking via the web/mobile site = 50 Yums
Each booking via the app = 150 Yums
1,000 Yums = $20 off your booking
2,000 Yums = $50 off your booking