Trading is the exchange of goods or services between two or more parties. So if you need gasoline for your car, then you would trade your dollars for gasoline. In the old days, and still in some societies, trading was done by barter, where one commodity was swapped for another. A trade may have gone like this: Person A will fix Person B's broken window in exchange for a basket of apples from Person B's tree. This is a practical, easy to manage, day-to-day example of making a trade, with relatively easy management of risk. In order to lessen the risk, Person A might ask Person B to show his apples, to make sure they are good to eat, before fixing the window. This is how trading has been for millennia: a practical, thoughtful human process.