Greenhouses don't grow. They are constructed of aluminum or steel framing and paneled with glass or plexiglas. If you're asking what you need to grow things in a greenhouse, you generally do not need anything special beyond the greenhouse itself, a substrate (such as soil) or a hydroponic setup, and a source of water if you are not using hydroponics. Greenhouses do not have to be heated during the winter, but you will be limited to plants that can tolerate cooler temperatures, such as radishes or lettuce.