Understanding what food is made of is important if you are to provide your body with the right balance of nutrients. But you do not have to know every last detail of the nutritional composition of your food, or even the biochemical processes your body uses to convert food nutrients into energy and muscle and bones. In a way, you can treat learning how to eat better as you would approach learning to drive a car. To drive, you need to know the traffic laws and you need to know how to operate the gas pedal, brake pedal, steering wheel, and turn signals. But you do not need to understand how gasoline burns in a car's engine or how the transmission works.
The saying "you are what you eat" refers to the idea that our diet and the food we consume directly impact our overall health and wellbeing. This means that the nutrients, vitamins, and minerals we get from our food choices are essential for maintaining a healthy body and mind.