You can buy coins, gems, chests, and card packs in the Store at any time. You receive card packs for defeating leaders and bosses in Story mode, and for completing Quests. You can also buy special hero packs in the Store. You can earn chests by completing dungeons in Story and Challenge mode, completing Secret Rooms and Locked Rooms and by purchasing them in the Store. Don't forget to check the Store for your free Mystery Chest.
You can earn free Gems in the shop by completing Tapjoy offers. Simply tap the "Free" gems and then follow the instructions provided by Tapjoy to complete the offer and receive your reward.