The classical conditioning paradigm asserts that if the mind is exposed to a neutral stimulus accompanied with a conditioned stimulus, then the mind will use memory to associate the neutral stimulus with the conditioned stimulus. For a modern example, when kids hear the chiming melody of an ice cream truck and they salivate. Whenever the truck passes by with ice cream, it plays a certain chiming melody, and thus the kids can learn to associate a direct connection between the ice cream truck arriving and the bells chiming.
The first stage of the classical conditioning paradigm entails exposing the mind to an unconditioned stimulus that will illicit a particular response independent of any other source. For Pavlov's dog, the unconditioned stimulus was food. When presented with food, the dog would drool saliva in anticipation of being allowed to eat. For the ice-cream example, the unconditioned stimulus would be the ice cream truck driving by the street and the kids seeing the truck. Like Pavlov's dog, a natural response for the kids to demonstrate when seeing an ice cream truck is to salivate.
The second stage of the paradigm entails the presentation of a separate, neutral stimulus in a manner that connects it with the original unconditioned stimulus. These two different stimulation devices should be related in time or location. For example, Pavlov rang his bell at the same time as presenting food (or slightly before) and thus Pavlov's dog would hear the bells at the same time as food was being presented. Also, because the ice cream truck chimes a melody while the truck is arriving, the kids hear bells at the same time that they see the ice cream truck and begin to salivate.
The third stage demonstrates the same response to the new, neutral stimulus even though the initial unconditioned stimuli is not present. Because Pavlov's dog could remember that, in the past, the arrival of the food was accompanied with bells ringing, the dog began to associate the ringing bells with food. When Pavlov rang the bells with no food present, the dog salivated as if food were present. This indicated that the dog had learned a direct relationship between bells and food. Likewise, because the kids learn to associate the chiming music with ice cream trucks, even if they are playing in the house and cannot see the street or truck, when the kids hear music chiming they immediately think that an ice cream truck is present and begin to salivate.