Hearthstone is a new trading card game online that allows you to pit your wits against other players.
They have some really cool characters from the Warcraft series that you can collect.
As you can see, the top left corner indicates the amount of mana needed to play the card. The yellow circle on the bottom left indicates its attack. The bottom right corner indicates its health.
The goal of the game is to defeat your opponent using your own set of 30 cards.
If you need a quick guide, you can find the Hearthstone card list here.