Skinner and Thorndike created experiments with animals. Thorndike formulated the following law: "any action that produces a satisfactory effect will be repeated". Thorndike makes cats in problem boxes that, when they behave in a way that disappears like boxes, learn and repeat themselves or move each time they were those only locations.
However, it was Skinner who developed the concept. Operational conditioning describes a correspondence between behavior and consequences. An operator response originated without the presence of an unconditional stimulus, that is, voluntary behavior. It will then be a process through which we learn the answers in order to avoid something unpleasant. But, consequently, the frequency of responses depends on the consequences.