To apply a PrintStick promo code, follow these steps: First, locate the desired PrintStick coupon code and copy it to the clipboard. Then, navigate to printstick.shop and place the items to be purchased in the shopping cart. During checkout, paste the copied promo code into the designated field. It's important to note that promo codes may have specific conditions or expiration dates, so it's recommended to use them promptly. If the code is valid and the conditions are met, the discount should be applied to the purchase.