Steroids in popular culture have a negative connotation due to the fact that they are often discussed within the context of athletes taking drugs to enhance their performance. However, steroids are simply a class of biomolecules that have a characteristic structure. Furthermore, there are many steroids that occur naturally in the body and they are necessary for normal body functions such as glucose regulation, ion absorption, and normal development.
Steroids are considered a type of lipid, which immediately suggests that its structure is dominated by carbon-based functionality and large chains of aliphatic groups. In addition, what characterizes a lipid as a steroid is the presence of four connected ring structures. All steroids have four fused rings, which are connected to various other functional groups. Of the the four rings, three are six-membered rings and one is a five-membered ring.
Out of all the steroids in the body, cholesterol is certainly the most abundant. The reason behind this is the various functions that it serves. One of the main roles that it serves in the body is as a precursor to other steroids, steroids such as the hormone steroids testosterone, progesterone, and estradiol, which are crucial in the normal development process. Cholesterol is also involved in the production of bile in the liver, which helps with digestion.
Steroids as Supplements 
There are two types of steroids that people ingest as a supplement. The first type of steroids are known as anabolic steroids. Anabolic steroids help build muscle, which is why they are often used by athletes and weight lifters. The second type of steroid supplement are known as corticosteroids. Corticosteroids are used as a therapeutic treatment for arthritis, and asthma, due to its role as an anti-inflammatory.
http://www.nlm.nih.gov/medlineplus/steroids.html Corticosteroid Treatment
http://biology.clc.uc.edu/courses/bio104/lipids.htm Lipids: Fat, Oils, Waxes, etc
http://themedicalbiochemistrypage.org/steroid-hormones.php Introduction to the Steroid Hormones