Materials are broken down by microbes. This process is called decay. This process occurs faster when conditions are warm and moist. Most microbes also need oxygen for decay to happen. The most important recycling occurs with the element carbon.
Plants remove carbon from the environment as carbon dioxide.
We eat plants, or other animals which have eaten plants, and the carbon becomes part of the tissues of our bodies as carbohydrates, fats and proteins. We respire constantly and release carbon dioxide back into the environment. Nitrogen is needed in our bodies to make proteins. When we break down proteins we remove them from our bodies as urea. All organisms have a similar process for the removal of protein products - this is because they are toxic to the body.