Before we get to the specific examples of the negative feedback loop, let's clarify some points. To begin with, you can say that it is a mechanism that helps to maintain the stable condition of an organism - homeostasis. Our body needs to adapt to the different types of environment and the negative feedback mechanism is one of the ways to do it. To put it simply, it is the process when some variable triggers a counteractive response to get an organism back to balance. Now, lets' consider some examples.
At first, let's explore the process of thermoregulation. During the summer period, people sweat a lot. That's because our nerves act as sensors and give the brain the specific signals. The temperature is the variable that changes. To get our body back to the balance, we use sweat glands. As the sweat evaporates from the body, we feel less heat. the process works vice versa as well. When you are cold, you may start to shiver. This process of muscle contractions can generate heat.
One more example of this process is blood sugar regulation. As the level of glucose increases, our body uses a specific hormone - insulin - to balance it out. Alternatively, if there is a glucose deficiency, the hormone called glucagon helps to increase its level. As you can see, our organisms do a great job at keeping us in the perfect balance.