Actually, composting is when cuttings and organic matter from food waste and leaves, is wetted down and layered in a pile perhaps inside a bin. After months, due to bacterial action, these materials break down into humus, technically not dirt, but, it is organic material found in soil, which is made of minerals from rocks that have weathered. Bacteria convert the materials into heat, carbon dioxide and ammonium, this ammonium further breaks down by bacteria into nitrites and nitrates. These substances act as fertilizer and help plants manufacture plant proteins and grow. It is recycling at its finest because instead of throwing out yard waste, it is converted to something useful to grow more plants.