Steroids (Roids) come in two forms with regard to humans: anabolic and corticosteroid.
Anabolic steroids are synthetic and used as a replacement for the naturally occurring hormone: testosterone. While there are legitimate uses for anabolic steroids (such as forced development of male characteristics like facial hair, deepening of the voice, and muscles growth), there are bodybuilders and athletes that abuse anabolic steroids to gain a competitive edge which is why the use of steroids is not allowed by nearly all of the professional sports bodies.
Coricosteroids, while also synthetic have a very different purpose the anabolic version. Corticosteroids are often used to treat inflammation and weakened or compromised immune systems. Individuals diagnosed with arthritis, asthma, autoimmune diseases (like lupus and multiple sclerosis), skin conditions (eczema and rashes), and some forms of cancer may find relief with corticosteroids.