Classical conditioning, also known as Pavlovian conditioning, is a non-conscious instinctual type of learning discovered by Russian scientist and Nobel prize winner Ivan Pavlov in the early 20th century. Pavlov hooked a dog up to a machine that measured salivation and rang a bell every time the dog was fed. Dogs naturally salivate when presented with food, but not when a bell rings. Over time, the dog began to associate the bell with food and would salivate whenever the bell rang, whether there was food or not. You can repeat this experiment at home with a willing test subject.
Find a subject who is a willing participant in your classical conditioning experiment. This could be a friend or sibling. You can also classically condition your own pet without being cruel by clicker training it.
Choose a stimulus. A stimulus is something that stimulates your subject's senses. For example, you could stimulate your subject's sense of hearing with a can of pennies. A can of pennies would be a negative stimulus, meaning that it would discourage behaviors because it creates an unpleasant noise. A clicker and a bag of treats would be a positive stimulus that would encourage behavior.
Choose a behavior that you want to discourage or encourage in your subject. For instance, you may want to discourage your dog from jumping onto your sofa or encourage it to sit when asked.
Respond with the stimulus every time the subject engages in the behavior. When the dog jumps on the couch, shake the can of pennies. When the dog sits when you ask, click the clicker and give it a treat.
Observe the subject as you repeat the experiment over and over. Eventually, the dog will associate the couch with unpleasant sounds and will avoid it entirely or it will sit on command if you click the clicker, even if you don't provide a treat. At this point, you will have classically conditioned the subject.