Sparks, Orbs and Free XP are the main "currencies" in the game.

Sparks are mainly used during Date gameplay in order to buy more cards in case you run out, or in case to use the Mirror and Chameleon cards more than once.

Orbs are the main fuel for upgrading Charms and Leveling up your girls, provided you've advanced either of the enough!

Free XP you can get either through regular gameplay and achievements, or from the Shop, from certain packs.

Free XP can be converted into XP for any of the girls that you've unlocked so far. You can extract free XP from a girl and pass it on to another, but this, however, will consume sparks.