How does Classical conditioning work?

Classical conditioning was studied by Pavlov and focuses on the learning process. Thinking about Pavlov's experiments with dogs, imagine: a dog salivates when he sees food - that is an unconditioned response (UR) because it happens naturally, without the dog having to learn that action. Therefore, the food here is an unconditioned stimulus (US). If we ring a bell ever time we presented the food - that is, we pair the stimuli - eventually the dog would salivate to the sound of the bell even when the food is not being presented and we would say that the learning process took place. The bell here is a conditioned stimulus (CS) because we need to condition the dog to salivate to it, the dog needs to learn to associate the bell with the food. For that reason the response - salivating to the bell - becomes a conditioned response (CR).