Your goal is to increase the Terraformation Index score and accomplish the various intermediary stages of planetary development. You do this by building machines that increase primary statistics of Oxygen, Heat, Pressure, and later Biomass in the form of Plants, Insects and eventually Animals (not yet implemented). The primary tech tree unlocks as you increase your Terraformation Index. Other tech items can be unlocked in each category according to their statistic, so you must balance what you are doing to gain access to all items.