To win Card Command you must defend your base while destroying the bases of your opponents. To do so, you must collect energy from treasure chests that spawn around the map. Use the energy to play the cards which you draw automatically approx every 10 seconds. Cards add additional varied units to your army, provide defensive structures for your base, grants advanced upgrades for your units, spawn computer-controlled foes to harass your opponents, and provide a large variety of other effects (including an alternate win condition).
To get you into the game quickly all players start with an all-random deck. This allows you to get to know the various cards. However, you have the option to customize your deck with a specialized combinations of cards to implement various advanced strategies. Decks can be saved and loaded in later games. You can also change your deck during the game (with a slight penalty) to allow you to adapt to opposing strategies.
Version 1.2 includes 61 different cards. Many more cards are coming in future updates!