Food is a resource in Empire Earth. 6 citizens are allowed to gather at a foraging patch at a time. Food can also come from granaries. Once the granary and all of its farms have been built, at least one citizen will automatically start farming. Only one citizen can forage on one farm at a time.. There is 8 farms in a granary so granaries are better ways of getting food for they have more farms.
Animals provide food for citizens to gather (if killed). Citizens can easily kill animals. Select a citizen and then right click on the animal. In Empire Earth, the citizen will shoot the animal with a gun and within a few shots, the animal will drop dead. In Empire Earth II the citizen will grab an axe and try to slaughter the animal.
To gather food from a granary you must have at least one citizen first. Right click on a farm (like gathering any other resource) and he/she will go and forage. The citizens stay put on a farm all of the time unless you tell them to leave.