The key function of classical conditioning is to allow an organism to

The key function of classical conditioning is to allow an organism to learn new species-typical behaviors.

Classical conditioning refers to when two or more different stimuli are joined in order for an organism to learn something it didn't know before. The more you repeat the conditioning, the faster the organism will learn. For example, Pavlov experimented with dogs - each time they were presented with food, they would also hear a bell. So each time dogs heard the bell, they knew that they would be getting food soon.