The energy we get from eating other organisms ultimately comes from the sun. Producers like plants convert the energy of sunlight into food for themselves and for the consumers.
Plants are a big group of producers, but not all producers are plants. Some bacteria and algae (pronounced AL-gee: simple plant-like organisms that live in water) have chlorophyll and use photosynthesis to make their own food just like plants do. These organisms keep a low profile, but they play a big role in producing oxygen and food in the world.