Compare classical conditioning and operant conditioning.

Pavlovian conditioning, primarily known as classical conditioning is a researching caused by the pairing of two stimuli regarding/involving animals. 

Operant conditioning is the reactions/behaviors of the animals consequences/effects on nature. 

Knowing this, we can essentially say that while classical conditioning is a learning process that pairs two stimuli, operant conditioning couples behavior and response with regard to the environment/nature. Another thing to note it that the learning processes of each are different too. In classical conditioning you can gain research before the response. However, in operant conditioning, the learning occurs after the response since we're looking at a cause-effect scenario.