A nutrient is something in food that gives you what you need to live and be healthy. For example, protein is a nutrient; you can find it in foods like milk, chicken, beans, cheese, seeds, nuts, and yogurt. For another example, vitamin A is a nutrient; you can find it in foods like pumpkin, carrot, sweet potato, spinach, broccoli, and bell pepper. (Yum.)
Foods like these are nutritious: they're full of healthy things that give you energy and keep you alive. And, these foods give you nutrition: they give you healthy, useful materials that the body needs. "Nutrition" can mean "healthy food," or "the things that make food healthy," but it can also mean "the study of healthy food," and "the process of eating healthy, or the result of eating healthy." If you have good nutrition, you feel strong and alert.