The free market is a summary term for an array of exchanges that take place in society. Each exchange is undertaken as a voluntary agreement between two people or between groups of people represented by agents. These two individuals (or agents) exchange two economic goods, either tangible commodities or nontangible services. Thus, when I buy a newspaper from a news dealer for fifty cents, the news dealer and I exchange two commodities: I give up fifty cents, and the news dealer gives up the newspaper. Or if I work for a corporation, I exchange my labor services, in a mutually agreed way, for a monetary salary; here the corporation is represented by a manager (an agent) with the authority to hire.
Both parties undertake the exchange because each expects to gain from it. Also, each will repeat the exchange next time (or refuse to) because his expectation has proved correct (or incorrect) in the recent past. Trade, or exchange, is engaged in precisely because both parties benefit; if they did not expect to gain, they would not agree to the exchange.