Compost is vegetable matter, rotted down so it can be used to fertilize and improve soil. You can make your own compost from lawn clippings, newspaper, food scraps and fallen leaves. Compost is best kept slightly moist, and turned regularly to aerate it. Worms in your compost will really help the composting process along, as the worms eat the food scraps and their castings become part of the compost.