As we are limited in space, below are a few ideas to help get you started. Let's focus on Ivan Pavlov's experiments with dogs.
In 1902, Ivan Pavlov, a Russian physiologist, discovered what led to his theory of unconditioned responses. Pavlov observed that his dogs salivated whenever they were being fed but even began salivating simply when Pavlov walked into the room, even if the dogs did not see food. Pavlov reasoned that salivating in the presence of food was a "hard wired" reflex for the dogs, or what we would call an unconditioned response. An unconditioned response is simply an unlearned response to stimulus, a response that happens naturally (McLeod, "Pavlov's Dogs"). Pavlov first developed an experiment to prove the dogs had an unconditioned response to food by giving the dogs bowls of food and then measuring their "salivary secretions" ("Pavlov's Dogs"). However, he also soon noticed that the dogs began to salivate, not just in the presence of food, but in the presence of anything associated with food. For instance, during the experiment, Pavlov observed that the dogs had no reaction to the lab assistant who fed the dogs; however, as the experiment progressed, he noted that the dogs began to salivate when the lab assistant walked into the room, just like they salivated whenever Pavlov came into the room. Since the dogs did not salivate in the presence of the lab assistant before but then began to, Pavlov was able to conclude that, while salivating for food is an unconditioned response, salivating in the presence of anything associated with food is a learned response. Pavlov deemed the lab assistant a "neutral stimulus," which is simply a stimulus that "produces no response" until a response is learned.
Pavlov then developed a second experiment to test his theory that neutral stimulus can produce conditioned, or learned responses. In his second experiment, Pavlov used a bell as a neutral stimulus. Anytime he fed the dogs, he also rang the bell. Several times, he fed the dogs while ringing the bell. At first, as expected, the dogs showed no response to the sound of the bell. He then tried ringing the bell on its own. By this time, the dogs began salivating when they heard the bell because by now they had learned to associate the sound of the bell with being fed; they had developed a conditioned response to the neutral stimulus of ringing the bell ("Pavlov's Dogs").
If we know that human beings as well as dogs can developed conditioned responses to neutral stimuli, we can use such responses to change our own behavior. It has been argued that emotional conditioning has been used throughout the ages to change our values, to change various cultures beliefs in what is moral and immoral (Prinz, "The Death of Morality: Morality is the Culturally Conditioned Response"). We can also use conditioning to change daily behaviors, such as encouraging a roommate to start being more cleanly. We might use a reward, such as promising to cook breakfast, if the roommate cleans her share of the room. In that case, cooking breakfast would be considered the neutral stimulus as it never would have induced the response of room cleaning before. However, as the procedure continues, if the roommate really wants free, pre-cooked breakfast, the roommate will become more and more conditioned to responding to breakfast by cleaning the room.