Reinforcement is any event that strengthens the behavior it follows and it can either be positive or negative. Many people believe positive and negative reinforcement to mean it is either good or bad, but that is not true. Positive reinforcement is increasing the behavior by presenting positive stimuli, so you can think of it by adding something. Negative reinforcement on the other hand is increasing behaviors by removing negative stimuli, so as to remove or take away something. This process is used in many different scenarios. Human beings and animals alike learn to adjust their behavior based on the type of reinforcement their behaviors receive.
Ten years ago, I got two yellow Labrador Retrievers and while I was training them I used positive and negative reinforcement to teach them when they were puppies. I would tell the dogs the commands that I wanted them to do, starting off simple with sit and shake. To reinforce the behavior that I wanted them to do I would reward them with a treat. So if they sat after I gave the command they would get a reward. This process was positive reinforcement. When I would give them a command and they did not listen I would not give them a treat. This taught them that they were not doing the correct thing. By using this process I was able to train my dogs to listen to the commands that I told them because their behavior was either getting positively or negatively enforced.
These concepts are related because my dogs were able to learn by their behaviors were correct by getting rewarded with a treat, positive reinforcement, or not getting a treat when they did not follow the command, negative reinforcement. Throughout the process of training my dogs with this tactic I was able to teach them many different things and reward them for doing the correct task.