Your Deck is a collection of Cards, used to duel against other decks.
Your deck and your hand are locations cards can be. They can only belong in one of them at once, i.e.they cannot be in both at once. Certain abilities will affect the cards within these locations.
At the start of the game, 4 randomly selected cards from your deck are drawn to form your starting hand.
Your hand is comprised of at most 4 cards from your deck. At the end of your turn, you draw cards to refill your hand back to 4 cards. Alternatively, a card's ability like Freebooters can draw cards during your turn.
Once a turn, you can replace a card from your hand with another one by dragging it to the left edge of the screen. This is called card cycling or shuffling and can be done anytime during your turn. In this process, you move one card from your hand to your deck and a random card from your deck to your hand. Note that playing a card, then shuffling or drawing a card can result in the same card being drawn, though there is a very low chance.
After going to the deck menu, there are 3 main sections: the available cards located at the top, your deck in the middle, and the collection button at the bottom.
The available cards acts like the collection interface, except it only shows 2 factions (Neutral and the deck's faction) and has a different layout (4x2). You can still sort by name, mana, strength, and movement, however.
In the middle, your deck is shown, along with other options to change the name of your deck and to select another one. While selecting a deck you also have the option to delete or create new ones. When creating a deck, you have to choose the faction for it first, and then you can add the cards in.
The collection button directs you to your collection.