That is where his profit comes from. Capital is wealth or money. But capital is not just any money. If you have crazy cash in a bag under your bed doing nothing, that's not capital. Capital is wealth on the move, it is money in power.
Capital is the boss money being used to make more money for the boss.
In order to understand capital, we have to ask a more basic question. The most basic type of wealth is the land. On the American continents, the Europeans came over here and stole the land from the native people who cared for the land and lived on it for thousands of years. Most of the European people who came over to live in the colonies were not the rich aristocrats and traders, but poor and working people. They had to work their asses off for many years to pay off their debt.