Second Earth has four types of resources you can harvest.
Ntrium is the main currency within Second Earth. It is used for the speeding up of tasks for building and upgrading, and it can also be used to purchase resources that you may not have. Ntrium can also be used to purchase premium items and to refill your hearts. While the game is pretty generous when it comes to providing this resource, use Ntrium wisely as you might quickly run out. Ntrium can be earned by completing quests, gaining achievements, acquired as daily login rewards, or buying them using real money.
Gold is used for buying and upgrading buildings. As well as starting multiplayer battles.
Plasma is used to hire troops, upgrading and buying some buildings, and researching upgrades.
Antimatter is used to build Captain IRON and Elite Troops.