The three sisters were corn, squash and beans. The Native Americans grew the food together. The bean vines would grow up the corn stalks and therefore would not have to be staked.
The Squash was planted between the rows of corn which eliminated weeding. The squash vines spread out covering the ground which kept the moisture in the ground.
These three vegetables were the mainstay of Native American Indians diets. They supplemented this diet with deer meat and other animal meat.
The Europeans did not grow their crops like this. When the Europeans arrived in America, they had a difficult time at surviving. The Native Americans taught them how to plant these vegetables and fertilize them using fish remains.
Corn, squash and other vegetables were introduced to Europe as what is termed the Columbian Exchange or the diffusion of culture. This changed the eating habits of people around the world.