Food is one of the main resources in which you use to keep your settlement growing. The main use of food is to construct buildings and maintain the upkeep of your military troops, and your population.
Food can be obtained by constructing a farm or a fishery within your settlement. Production can be enhanced by a Processing plant. Additionally, it can be recieved as a trade from other players, or another one of your settlements by using a Customs house. You may also recieve 100 food from the random resources each one of your Wonders create daily (1,000 food may also be obtained from The Colosseum wonder daily).
Food production can also be boosed by capturing a Food tile.
Food is used to feed your armies and troops to make them fit and healthy enough to wade of barbarians, raid or capture tiles. A higher population will also decrease hourly food rate, but can be boosted back up by capturing Luxuries.