The buildings that you or your colonists build independently produce raw materials, industrial products and strategic units, like tanks, explorers and missiles. You can use them for the needs of the colony or sell them in the Interplanetary Exchange. If you can’t or don’t want to produce them in your colony you can also buy them from the exchange.
Every transaction you make affects the price of the product. If you or a competing colony buys for example a lot of fuel, the price will go up and purchasing it will become more expensive. Selling of the product in turn lowers the price. It is possible for you to win the other colonies economically by making smart trade decisions so that the prices of the products they buy are high and the prices of the products they sell are low.
If you have extra cash, you can make deposit to the Interplanetary Bank. If you need more cash for purchases or to support your society, you can also borrow it from the bank. The amount of deposits and loans affects the interest rates. Interest is paid for deposits and charged for loans.