Primary and secondary reinforcement are both forms of positive reinforcement which is the process of rewarding a behavior. Primary reinforcement involves a reward that fulfills a biological need. Secondary reinforcement is reinforcement associated with the fulfillment of that need.
Primary reinforcement fulfills a biological need; examples include food, shelter, water and the like. Giving a dog a treat for sitting down is an example of primary reinforcement.
Secondary reinforcement is associated with the fulfillment of a biological need. For example: If a dog owner were to give his pet a treat for sitting down, and the dog began to associate the sound of the bag opening with the treat, the dog would be responding to secondary reinforcement. The sound of the bag is a reminder of the primary reinforce (i.e. the treat), thus just hearing the bag open may cause the dog to sit.
Example of Primary and Secondary Reinforcement in Action
A child goes to touch a teapot that is whistling. The child hears the whistle (secondary reinforcer), touches the teapot and is burned (primary reinforcer). The child will begin to associate the whistling sound with a hot teapot, as she was burned, (a positive reinforcer), she will avoid touching whistling teapots.