What is value adding?

In economics, the difference between cost of materials and labor to produce a product, and the sale price of a product is the Value added. In national accounts used in macroeconomics, value added is the contribution of it refers to the contribution land, labor, and capital goods (the factors of production), to increasing the price of a product, the value added is then the income received by the owners of these factors. The national value added is shared between capital and labor (as the factors of production), and this sharing gives rise to issues of distribution.

sources: http:/en.wikipedia.org/wiki/Value_a