The Farmer's House allows you to produce Food in your City. It also increases the maximum amount of Food that is protected from your enemies. This building is essential for increasing your Capitol's level.
Food is used to train troops and to maintain your army. It can also be converted into Religious Tractates in Clan Temples. It is also used to charge the Shield of Peace over your Clan Capital.
All troops in your City, except for allied reinforcements, consume Food. If the amount of Food being produced is lower than your army upkeep cost, then your Food counter will turn red, and your City will receive the Food Deficit debuff, which increases the cost of training troops. The greater the deficit, the greater the cost increase. If the amount of Food in your City reaches zero, your City will receive the Hunger debuff, which decreases your army's strength and health by 25%.