We depend on light energy or solar energy for food because we get the our food from plants which in turn depend on the sun for their food. As in animals, the herbivores eat plants which make food using energy from the sun . Omnivores and carnivores also depend on plants. However they eat animals but the animals they eat depend on plants. Green plants are the producers. They are also known as autotrophs.
Solar energy produces food, wood (plants need sunlight to grow and make food, so trees produce wood and indirectly the sun produces wood) which are used to get fossil fuels.
There are also some renewable sources of energy which do not depend on Sun they are Geothermal energy , etc.