Calorimetry is like using a special scale to measure how much energy food gives you. Imagine you have a cookie and some milk, and you want to know how much energy you'll get from eating them. You can't just guess, so you need a way to measure it. That's where calorimetry comes in!
Calorimetry works by putting the food and drink in a special container that's insulated, or covered in material that doesn't let heat escape. Then, you measure the temperature of the container before and after you add the food and drink. The temperature will change because the food and drink have energy in them, and they give off that energy as heat.
By measuring how much the temperature changes, we can figure out how much energy the food and drink have. Just like how you measure weight with a scale, you measure energy with calorimetry! Scientists use calorimetry to figure out how many calories are in different kinds of food and how much energy people need to eat to stay healthy.