Yes! Doing promotions where you give away your book for free or at a discount is an important part of marketing books.
To create coupons, go to the Book Tools menu for your book and click on "Selling & Royalties" and then select 'Coupons'.
You can set various parameters for the coupons you create, including coupon price, maximum number of uses, start date and end date. Anyone you give a coupon link to can use it to buy the book at the discounted coupon price. If you set the coupon price to zero, they can get the book for free, like a review copy.
Please note that our start dates and end dates are set to the UTC time zone. If you are planning a sale, for example, from March 12 to March 14, we recommend you set the start date to March 11 and the end date to March 15.