Hardcover is usually used for books with more pages, frequent use, long-term preservation, aesthetic requirements and more important books. There are three forms of hardcover: (1) round back hardcover, (2) square back hardcover (or flat back hardcover) and (3) soft face hardcover.
If you want to know the specific difference between hardcover cover and paperback cover. You can learn more about the differences by using the hundredth library of Appreciation of Book Cover Design-Cover Publishing Every Day in the World.