In Classical conditioning, learning occurs when a neutral stimulus is paired with an unconditioned stimulus, the neutral stimulus becomes a conditioned stimulus which can bring about conditioned responses.
For example, unconditioned stimulus (food) is presented repeatedly just after the presentation of the neutral stimulus (bell). After conditioning, the neutral stimulus alone produces a conditioned response (salivation), thereby becoming a conditioned stimulus. From this example, if a dog salivates whenever it sees food but a bell is rung before the food is presented, Overtime just ringing the bell will make the dog to salivate.
