In the Paleolithic age we obtained food by hunting and gathering. Hunting was dangerous and hunters could injured and even killed. And if we stayed in an area for too long all of the plants would grow scarce. we were not able to rely on this food source.
We then realized that we could plant the seeds of food to grow crops.
They learned that if they domesticated animals they could raise them and eat them. Also they could milk some animals and even use some to help farm.