Capitalism is based on the idea of capital circulating freely between people who own companies. In capitalism, you make goods and are not as much controlled by the government and as such people belonging to a capitalist society buy goods from manufacturers and the money keeps circulating between producers and consumers.
In socialism, the manufacturing and producing companies are owned publicly by people, or more precisely by the state which represents the people. The state cares about production so that people get what they need and how much of it they need, instead of just making whatever kinds of good people are willing to throw their money on.