Protoss and Zerg building construction is limited to specific locations: Protoss buildings need to be linked to a power grid while almost every Zerg structure must be placed on a carpet of biomass, called 'creep', that is produced by certain structures.
Although the nature of the supply differs between the races-Terrans use physical supplies held in depots, Protoss use psionic energy channeled from their homeworld via pylons, and Zerg are regulated by the number of controlling overlord units present -the supply mechanic essentially works in exactly the same way for each race (just with differing impacts on gameplay), allowing players to create new units when there are sufficient resources to sustain them. In addition, players need to regulate the supplies for their forces to ensure that they can construct the number of units they need. Players require vespene gas to construct advanced units and buildings, and acquire it by constructing a gas extraction building on top of a geyser and using worker units to extract the gas from it.
Minerals are needed for all units and structures, and are obtained by using a worker unit to harvest the resource directly from mineral nodes scattered around the battlefield. Each race relies on two resources to sustain their game economies and to build their forces: minerals and vespene gas.
