During a game, the player must use workers to gather minerals and vespene gas. Minerals appear as blue crystals in the ground and vespene gas comes from a geyser that has green smoke coming out of it. To gather vespene gas, the player needs to build a refinery building to be built on the geyser. The player uses minerals and vespene gas they have gathered to construct buildings and create units to fight the enemy. Buildings are structures that are used to create different kinds of units to fight the enemy. In order to create units, players must build special structures or units that provide "supply". If the player does not have enough supply, they cannot create more units. Each player has a supply limit of 200 units. When the player has reached 200 units, they can not make more units.