The rich humus formed by composting is not only a vital part of good soil but also the cheapest soil conditioner available and the easiest to obtain because you make it yourself. Without it, plants will not flourish no matter how much love and attention are lavished upon them. Even if you don't have room for a full-fledged heap, you can still compost in a plastic bin. Nitrogen-rich materials include most fresh, green forms of vegetable matter, such as kitchen peelings, green leaves, and grass clippings.
Paper is also rich in carbon.
Oxygen is absorbed from the air , so the heap must be turned regularly, or, if it is enclosed, provision should be made for air to penetrate through the sides. Too much water is as bad as too little excess water will decrease the amount of oxygen in the heap. To keep the heap damp but not wet, cover it. If it starts to dry out, you can add moisture for a few minutes by fine spraying with a hose. The interaction of all these elements , combined with the heat generated by microbe activity, breaks down the organic matter.