The textbook talks a lot about contingencies and the four different types. Two of them being positive and negative reinforcement. Both of these things most of us should be familiar with from experience, even if you have not heard of it before taking this class. Positive reinforcement is defines as the presentation of a stimulus (one that is usually considered pleasant or rewarding) following a response, which then leads to an increase in the future strength of that response. Negative reinforcement, on the other hand, is defined as the removal of a stimulus (one that is usually considered pleasant or rewarding) following a response, which then leads to a decrease in the future strength of that response.
Both of these reinforcements can be beneficial depending on your situation. For example, if you're a teacher and you have a student that does well on a paper and you want her to continue to put forth the same effort, you will praise that student individually on how well she did on the paper. this would be considered positive reinforcement. an opposite situation would be if a student did not do their homework but you want them to do it in the future, for that specific homework assignment you will give them a zero to encourage them to actually do their work the next time. this would be considered negative reinforcement.