Operant conditioning is a method of behavior modification using positive and negative reinforcement. B. F. Skinner is the behaviorist who first discovered and employed this type of conditioning; it works upon the principles of reinforcement and punishment, both of which have positive and negative consequences.
With regard to positive reinforcement, there are rewards for behavior that is desired. This is called appetitive stimulus; for example, the child who behaves in a desired manner is treated to something she desires. With negative reinforcement, there is a conditioning of the subject to avoid some type of painful experience, physical or psychological.
With regard to punishment, there are both positive and negative aspects, as well. An example of positive punishment involves a negative consequence given after undesirable behavior is exhibited (e.g., a scolding). Negative punishment involves a type of removal of a pleasant experience given after undesirable behavior is exhibited (e.g., the loss of a privilege).