The currency of HPS is coins and gems. Coins are more common and buy most items, while Gems are rare and are used to purchase gem specific items. Both can be purchased for real money.
Coins can be earned for completing quests and games, visiting townies and friends, and sharing pictures. Any items purchased or gifted to you can be sold back to shop merchants for coins as well. Coins can also be found outside around town in the form of bugs, chicks, and inside of balloons.
Occasionally, a bug or chick will give a Gem instead of a coin. But are primarily given as rewards by the mayor or from leveling up.