A little rundown on the mechanics, because we didn't have time for a tutorial, but apparently the game really needs one:

each card has a type (dark/light, you can identify it by the card's bg color) and drains mana from a corresponding circle when you place it, the cost of the card is the number of dots at the top of the card, it's damage is the number to the left of that,  and the arrow points to a column the card will hit

cards that are placed in the first row (card's row indicator is under the cost) do damage to the oposing column (remeber about the arrow),  the damage is dealt from bottom to top (if all damage gets used on a card, nothing behind it gets hit) for your cards, and top to bottom for enemy, if card hits another card, it lowers it's damage, cards with 0 damage get destroyed
cards in the second row usually do support stuff like healing you, adding damage to your cards or regenerating mana, you can understand what the card does from the description
 the goal of each battle is to bring the opponents health to 0.