Opioids are either are derived from the opium poppy or produced from chemicals to provide or intensify the effects of natural opium. There are many different opioids, including morphine, heroin and codeine. They can be manufactured in regulated labs and used for medical treatment in and outside of hospitals, but they can also be made in illicit labs by people with varying degrees of competence.
Heroin is a depressant or downer. It slows your body and can make people feel relaxed.