Your body needs nutrients to keep you alive. Getting the right balance of these nutrients has a dramatic impact on the results you desire. Almost all your nutrients come from the food you eat. The nutrients you need in large quantities are called macronutrients. There are three kinds of macronutrients (aka "macros"):
The nutrients you need in tiny quantities are called micronutrients, and include things like vitamins and minerals that your body needs to carry out its daily functions.
In a very broad sense, macronutrients supply you with your energy, and micronutrients help your body unlock and use that energy.
Each of the macronutrients supplies your body with a certain amount of energy, that is usually measured in either kilojoules or calories (which are more commonly used).