Ate you asking why people take supplements of why they take drugs/PEDs?
Supplements are supposed to be what the name implies...a supplement to your diet. Foods, proteins, vitamins and other ergogenic aids are all included. Can include the basics like protein or creatine to preworkout stimulants and of course, stuff like prohormones that are now banned but were once over the counter.
Some work, some don't but they pretty much all give you that mental edge because you want to believe they're working. In some cases, that's enough. There's also the tricks the companies use, like adding niacin to a preworkout so that you get that warm flushed face feeling to make you believe somethings happening.
One thing is for sure, don't believe all the crap you read in the mags...nothing will give you "steroid like results" except actual steroids.