In ecosystems, energy usually flows from the through to

Sun/inorganic compounds
autotrophs (producers)
heterotrophs (consumers)

The sun is the main sources of energy. The energy in the form of sunlight is converted into a form of energy that organisms can used. Plants converts sunlight into their food through photosynthesis. Plants will be considered as the producers. They will be eaten by herbivores or the heterotrophs/consumers. Energy can now be transferred to the consumers because they cannot utilize sunlight to form their own food.