Resource Buildings (steel mill, farms, mineral mines, oil refineries)

What are the resource buildings and how do I use them?
There are four resource building types. They unlock as your City Hall levels up. It's a good idea to keep upgrading all of your buildings because it adds to your overall battle power.
 * Farms
 * Oil Refineries
 * Steel Mills
 * Mineral Mines
 * Power Ore Mines

For a walk through of how to check your resource your resource output, watch this quick video by Son31llon.