There are 3 sources of food in Village Sim: the berry bush, which is always available (although the berries run out); the farm, which requires level 2 of Harvesting (teach some villagers to research at the research table to get enough points); and fishing, which requires level 3 of Harvesting. It's important to research Harvesting technology before the berry bush runs out of berries or your villagers will starve.
There's a pretty good discussion about the various aspects of getting food in
this thread.