By using a counterconditioning and desensitization plan, you can change an animal's unpleasant emotional response to a trigger into a pleasant one by exposing the animal to the fear trigger in a gradual, incremental manner and offering rewards, such as high-value treats, once the animal is relaxed.
Classical conditioning, like counterconditioning, creates an association between items through exposure and rewards. The difference is that in classical conditioning, a dog does not necessarily have a negative association with one of those things. The best example is Dr. Ivan Pavlov's dogs: A bell was rung, and the dogs were presented with food. Once the connection was made, the dogs salivated at the sound of the bell.