Macronutrients AKA "macros" are the 3 main building blocks of any food: Carbohydrates (Carbs), Fat, and Protein.
Learning to 'track' macros is a popular nutrition method to support your health and fitness goals. Depending on your goals and lifestyle, including if you're vegan or on a plant-based diet, the most optimal amount of protein, fat and carbs for you changes.
Tracking macros means you can dial in your diet to your specific nutritional and physiological needs. Because your macronutrient targets act as guidelines or guard rails, you're still able to be flexible with your food choices. So much so that macro-tracking is often referred to as "flexible dieting".