Promotions can be applied to a transaction in a variety of ways:
Discounts are applied to a transaction automatically when a promotion is applied. The value of the discount is dependent on how tax is calculated in your region, see How Promotion Discounts Are Applied to Transactions.
Free gift SuitePromotions automatically add the free item to a transaction. Promotions that offer an item or items for free – but are not created using the free gift SuitePromotion type – do not automatically add the item to a transaction. For more information, see Applying Automatically Added Free Gift Items.