The playing system in HearthStone is similar to other titles of the genre, like Magic: The Gathering. You receive an additional mana point each turn, which allows you to play more cards. You can call on creatures to attack your opponents, cast powerful spells, and combine all of your abilities to perform powerful moves that will finish off your enemy and all of their health points.
You can play in individual duels over the Internet, or try your hand against the computer - but maybe the most interesting playing mode is the Arena, where you are assigned a random deck of cards and must try to survive the greatest number of duels using just that.
The most important part of HearthStone may be the battles against other players, but it's not the only part of the game. Collecting the cards themselves is also very important, and you can even buy packs of cards to add to your deck. To get the money needed to buy more cards, you need to win your battles... or pull out your wallet and pay with real money.
HearthStone is an outstanding collectable card game - maybe the best of its genre. In fact, the only problem it has is that it's so good, it will eat up all of your free time. Trust me, I'm speaking from experience.
To play, you'll need to create a free account on Battle.net, Blizzard's online game service.