To use a Saint Lyon coupon code, first add the desired items to your shopping cart on the Saint Lyon website. Navigate to our website and select the Saint Lyon promo code that suits your needs. Click on the 'Get Code' button to save the code. Go back to your shopping cart on the Saint Lyon website and enter your details. Look for the 'Enter Promo Code' section and paste the code you saved earlier. This will instantly apply the discount to your order.