He put cats in "puzzle boxes", and the cats would have to learn how to escape. - The reinforcer would be the cat breaking free!

If an action brings a reward then the action becomes stamped into the mind. Behavior is changed because of it’s consequences.

Thorndike's Law of Effect:

Behaviors followed by  favorable consequences become more likely, and behaviors followed by unfavorable consequences become less likely.

Perhaps one of the most famous psychologist to ever lived. He worked with rats in "skinner boxes."   

He trained a rat to do a wide variety of tasks: the most basic task was pressing a bar to obtain a reward of food. Once the rat learned how to press a bar, the rat can be taught to only press the bar when presented with other complex stimuli.   Using this situation it is possible to measure how well the rat perceives, learns and remembers, therefore, many psychological variables can be investigated in rats.

Reinforcer – increases the likely hood of a response.  Primary or secondary reinforcers can be delayed or immediate.

Primary (innate) food, relief from pain (a negative Reinforcer)

Secondary (Learned) – money, not necessary, something that can be traded in for a primary Reinforcer (symbolic)

Immediate - Much more effective than delayed reinforcers.
Example: It is better to add a dollar to a piggy bank toward a bicycle every time the child brings home a good grade, rather than waiting until the end of the year, and if the child has a good GPA, then giving the bicycle. Immediate reinforcement is better than delayed reinforcement perhaps because the child is not able to keep the goal in his or her mind without being regularly rewarded for the the desired behavior.

A punisher – decreases the likelihood of a response.

However - For some children, being yelled at may be seen as reinforcement. Although parents perceive yelling to be a form of punishment, a child may find this a positive reinforcer because the child is looking for attention.

procedure which rewards the animal, gradually guiding its behavior toward a desired behavior  Imagine that you want to condition a rat to press a bar. You might give the rat food every time it comes close to the bar, then start narrowing down the reward area until the rat only receives a reward when it touches the bar. Eventually you only give rewards when the rat pulls the bar all the way down.

The animal does something that you did not intend for it to do, but it also does the thing that you want, a compound action.  For example, the rat hits it's head on the wall before it hits the bar, therefore making the rat think it needs to hit it's head and push the bar to receive a reward.  In humans this is observed in such behavior as the expression of  "knock-on-wood" thinking that the phrase will increase the likelihood of a favorable outcome.

If you use techniques too much, a person who would have done something for their own satisfaction, then does something simply for the food/money.