Paint is made from a coloured pigment which is usually a powder. The powder is made from different chemicals. Some of the pigments come straight from natural things like clay. The pigment must be made wet by mixing it with something that will make it stick onto the surface and not come off easily. The wet stuff is called the "medium" or "vehicle". Some paints are just mixed with water. Other paints are mixed with oils or chemicals of different sorts. Most painters buy paint that is already mixed. House-painters use paint already mixed in large cans. Artists buy paint in tubes. Some artists buy dry pigment and mix it for themselves.