The service announces its own campaigns for new riders. They run in Tashkent and in several cities of the Fergana Valley, cover the first rides and cap the discount on each ride. In those campaigns the discount is counted automatically, so nothing has to be typed at checkout.
The code on this page does something else: it is an invite code that tells the app who referred you. The exact discount and its end date appear only inside the app, in the ride discounts section, so open that section before your first order. A code is used once, cannot be moved to another account and is not exchanged for money.
Every offer has a page of its own with the cities it covers, the date it ends and the limits that apply, based on the campaign rules Uklon publishes. The service can change those rules, so compare them with the text in the app before you confirm a ride. Other ways to get around the city sit in the travel section, which also collects scooter offers.