Value-added Problems in Capital Theory

In other words, a laborer (that is, a hired worker) works for one day, but his salary is only half of the value he creates. So where is the surplus value? -occupied by capitalists.

This is Marx's theory of surplus value. One of the essence of capital is to pursue value appreciation, but it is impossible to realize value appreciation through commodity exchange and circulation. Therefore, capitalists must extend the absolute labor time of hiring workers-the extra labor time is value added, that is, surplus value.

I'm just saying it briefly. If you are interested, you can look at the first volume of Das Kapital, which has a very detailed discussion.