To apply a discount code to an order on the Warner Brothers Online Store, first, you would need to add the desired items to your shopping cart. Once you have finished selecting your items, proceed to the checkout page. At this stage, you should see a field or section labeled "Promo Code," "Discount Code," or something similar. Enter your discount code carefully in that designated area, ensuring there are no typos or unnecessary spaces. After you have entered the code, you may need to click on a button to apply the discount. The page should update to reflect the discount deducted from your total amount. If the discount code is valid, you will see the adjusted price show up in your order summary. If you encounter any issues, you might want to refer to the current web page for help or any specific terms related to the discount code.