There are two forums of currency, Treasure and Gems.
Treasure you can get from playing games and exalting dragons and hoard selling items. Gems mostly originate from being bought with USD, but very small quantities are gained every day if your dragons are well fed or sometimes randomly from exalting dragons.
Treasure is the primary currency, but gems have a lot of very unique uses that makes them sought after. So there's like a floating conversion rate between them. 1:600 is 1 gem = 600 treasure. It's a little like TBT:IGB. TBT is the special currency that you can do lots of things with (buy things from art shops, collectibles, formerly game codes, etc), but IGB is the currency eeeeveryone needs to play the actual game.