Resource is a general term that applies to anything in the stockpile. There are two general types:
Infinite resources are just that- infinite. Iron Mines, Quarries, and Pitch Rigs never run out of material. They will keep producing until unable to (which is a result of its destruction, running out of labor, or a full stockpile).
Stone is used in the construction of walls, towers, barracks, and gatehouses. Quarries generate large amounts of stone very rapidly. After the fortress walls have been established, this can be a wonderful source of income.
Pitch is used only for pitch ditches. Large amounts of pitch rigs (about seven or more) can provide a moderate source of income.
Wood is used in the construction of most buildings in Stronghold and . A small Wood Camp is all that is needed; a single trip will provide twelve planks. Wood is a poor source of income, as it does not bring a high price, and there is only a limited supply on any given map.
Hops Farms grow hops for breweries. A single farm can grow enough hops for about four breweries. Before brewing, hops are placed on the stockpile, appearing as a pot of green material.
Ale comes in barrels. A brewer will take a pot of hops and brew them, rolling the resulting barrel back to the stockpile. Ale is used at inns, and is a wonderful way to boost popularity.