An autotroph is an organism that makes its own food from light energy or chemical energy without eating. Most green plants, many protists (one-celled organisms like slime molds) and most bacteria are autotrophs. Autotrophs are the base of the food chain.
It is impossible to make food from energy alone. I stole the following quote from an encyclopaedia website. "Photosynthetic autotrophs include the green plants, certain algae, and the pigmented sulfur bacteria (see photosynthesis). Chemotrophs include the iron bacteria, the nitrifying bacteria, and the nonpigmented sulfur bacteria (see chemosynthesis). Heterotrophs are organisms that must obtain their energy from organic compounds."