According to the newly launched website, Scrolls "offers a new and unique game play where you fight to outmaneuver your opponent on the battlefield [a chess-style game board] using the destructive powers in your collection of magical scrolls [cards]." Scrolls will become weathered with use, giving visual indication of your preferred tactics. Of course, you'll be able to augment your deck with new packs.
A limited free alpha will be available later this year, offered initially to some Minecraft alpha purchasers; a public beta willfollow. Both will be free and used to balance the game.