From Civ World

Production is one of the five major resources in Civilization World. Production is generated by Workers working in the City or can be purchased from the market, and is used to build new Buildings and Military Units. Production is stockpiled automatically and can be spent by visiting the Build Menu from within the City screen.

• Citizens in the city can be assigned the job "Worker" to produce Production.
• Workers working in the city require at least one raw resource patch nearby. This can be either a Forest, a Stone Quarry, or an Iron Mine.
• Workers working in the city gain a boost from nearby buildings depending on what type of raw resource they are working:
  • Workers working in a forest gain a boost from a nearby Lumber Mill.
  • Workers working in a stone quarry gain a boost from a nearby Stone Mason.
  • Workers working in an iron mine gain a boost from a nearby Iron Forge.
  • Workers working with any production resource with a nearby Factory will gain an even larger boost than either the Lumber Mill, Stone Mason or Iron Forge.