Agriculture is the intentional growing of plants for human use.
Agricultural societies appeared in several widely separated parts of the Old and New Worlds over 5000 years ago. Most human populations had become dependent on agriculture by some 2,000 years ago .
Various amounts of care are involved, from little more than scattering seeds and later checking for a harvest, to large scale industrial agriculture, where thousands of acres are devoted to growing one crop, using carefully bred and selected seeds, highly processed man-made fertilizers, and a variety of pesticides.
The plants themselves have been selectively bred since the early days of agriculture for many characteristics, including fruit size and yield, disease and pest resistance, drought or wetness tolerance - in fact, any trait that could be imagined to be useful.
While it is immediately obvious that the first purpose for growing domesticated plants is to provide a stable food supply, we also grow plants for fibers to make clothing, to press for oil, or to make into paper. Plants are also grown for real or perceived medicinal properties, like tobacco or poppies.
By tying a community to the location where its crops are planted, and making the production and storage of surpluses possible, agriculture led to the development of villages and cities, and the need for, invention, and development of civilization itself.