What is art? Art is something you can: sculpt, sketch, draw, paint, spray paint, collage and so much more.
People sell art because they may want money or some people do it for fun. Whatever the reason most people sell art to raise money for something.
Some people buy art to decorate their homes because their homes are bare and dull, so they buy something worth value. A lot of people buy art because they want something new.
That is why people buy and sell art.