Autotrophic nutrition involves the use of an external energy source to make the complex organic molecules that we call food from inorganic substances
The organism that carry out autotrophic nutrition are called autotrophs.
Plants use light energy from the sun as their external energy source, this type of autotrophic nutrition is photosynthesis.
During photosynthesis carbon dioxide and water are used to manufacture carbohydrates.
Light energy is trapped by chlorophyll and used to fix carbon dioxide, firstly to reduce it to carbohydrates.
Plant manufacture all the other organic molecules that they need from these carbohydrates and very small quantities of mineral ions obtained from the soil.