Operant conditioning is the use of consequences to modify the occurrence and form of behavior. It's important to note that organisms are not spoken of as being reinforced, punished, or extinguished; it is the response that is reinforced, punished, or extinguished. Additionally, reinforcement, punishment, and extinction are not terms whose use is restricted to the laboratory. Naturally occurring consequences can also be said to reinforce, punish, or extinguish behavior and are not always delivered by people.
Positive reinforcement (Reinforcement) occurs when a behavior (response) is followed by a favorable stimulus (commonly seen as pleasant) that increases the frequency of that behavior. In the Skinner box experiment, a stimulus such as food or sugar solution can be delivered when the rat engages in a target behavior, such as pressing a lever.
Negative reinforcement (Escape) occurs when a behavior (response) is followed by the removal of an aversive stimulus (commonly seen as unpleasant) thereby increasing that behavior's frequency. In the Skinner box experiment, negative reinforcement can be a loud noise continuously sounding inside the rat's cage until it engages in the target behavior, such as pressing a lever, upon which the loud noise is removed.
Positive punishment (Punishment) (also called "Punishment by contingent stimulation") occurs when a behavior (response) is followed by an aversive stimulus, such as introducing a shock or loud noise, resulting in a decrease in that behavior.
Negative punishment (Penalty) (also called "Punishment by contingent withdrawal") occurs when a behavior (response) is followed by the removal of a favorable stimulus, such as taking away a child's toy following an undesired behavior, resulting in a decrease in that behavior.

Bibiliography:http://en.wikipedia.org/wiki/Operant_conditioning