During Gameplay you will collect several themed decks and it is important that you understand the purpose of each one of them so you know when it is the best time to use them. At the start of the game your deck will be made up entirely of neutral cards that can be used in any deck you want to create. You will start to get themed cards once you begin earning gold coins and getting card books.
Each deck will consist of 12 cards and a good strategy when deck-building is to only have one or two high-cost cards and three or four 2-3 cost cards in your deck. The benefit of making your deck up like this is that it enables you play two cards at once the first round which should give you an immediate advantage. It is also a good idea to have one or two instant damage cards and/or buildings.
You will continually draw cards no matter how many you have already used but you will only be able to have 4 cards in your hand at once when playing your turn.