A Unconditioned stimulus is a stimulus that automatically gets an emotional response from the person, without having to learn it before hand. Like smelling something nice, like your favorite food makes you hunger.
Unconditioned response is a unlearned reflex that happens when meet with the unconditioned stimulus. Like touching a hot oven, you immediately take your hand way because you body recognizes it to hot.
Conditioned stimulus is a stimulus that is no longer neutral, the conditioned stimulus now getting paired with the conditioned response out of habit. Conditioned response is a learned reflex