Frank and his dog are relaxing in their backyard gazebo. As you can see, a bell is on the table. At this point, the bell is the neural stimulus as it does not provoke any response from the dog; thus no response.
During Conditioning
Frank rings the bell right before giving the dog some food. Frank repeats this everyday throughout the week. At the start of the week the dog was not conditioned to the sound of the bell and receiving food. This would mean that the unconditioned stimulus was the food and the unconditioned response is the dog salivating. However, at the end of the week the dog connects the bell ringing to receiving food. Thus, the conditioned response is the dog salivating and going to the neutral stimulus and the conditioned stimulus is receiving food.
After Conditioning
This time, the Frank rings the bell, but there is no food present. However, the dog still begins to salivate when it hears the sound of the bell. This is the conditioned response - a learned response to the conditioned stimulus (the bell). The dog has now been conditioned to associate the sound of the bell with the arrival of food.