Magento Coupon Gift Product adds gift product when specific coupon code applied. The coupon code can be created using magento default sales rule at the admin Promotions -> Shopping Cart Price Rules. For usage gift product please select option Apply: Add Gift Product at the Actions tab. Then you need to leave Discount Amount as 0 because it required field and fill Gift Product Sku with sku of the gift product. Field set gift product price 0 will force gift product with zero price this way it can be used for free gift by coupon.