Behaviorism is a learning theory that states all behaviors are acquired through conditioning, which occurs through interactions with the environment. There are two types of conditioning - classical conditioning, where a stimulus is paired with a response, and operant conditioning, where behaviors are reinforced through rewards or punishments. Key figures in behaviorism include Ivan Pavlov, B.F. Skinner, Edward Thorndike, John B. Watson, and Clark Hull. Behaviorism can be applied in classrooms through techniques like rewarding good behavior and punishing bad behavior.