Steroids are drugs which mimic the male sex hormone (testosterone) and in turn, give your body the capacity to build greater amounts of muscle much easier than without this exogenous source of foreign testosterone.
Pro-hormones are drugs which are chemical cousins of steroids which once metabolized in your body, convert chemically to some sort of steroid and thats when they mimic testosterone. Because they must be metabolized first, they are more inefficient at converting into testosterone that real steroids.
Growth hormones or HGH stimulates growth, cell reproduction and regeneration in humans. Its tough for me to describe the difference between steroids and HGH, but there is a vast difference. Essentially steroids mimic testosterone and HGH is a whole different pathway for growth in our bodies and HGH promotes growth of everything including bones, cartilage, muscle, fat reduction, and organ enlargement while testosterone only promotes growth in skeletal muscle while providing an array of testosterone induced side effects like acne, excessive hair growth, and in very rare cases aggression.