Add your selected tickets to your cart, and when you get to the checkout screen you will be able to apply your promo code in the prompt, where it will automatically apply for you. Only one promo code can be applied per booking.
If you have a Latitude gift card, these can also be applied at the checkout screen.
Supaworld gift cards and vouchers can be used to make a booking over the phone, or they can be used in venue. Unfortunately they can no longer be used to book online.