P.cubensis grows wild across much of the world. In the wild it feeds on and fruits from the dung of mammals and usually produces small to medium-sized, light-brown fruiting bodies, though there is a lot of natural variation. It is the best-known, and perhaps most widely-used member of a genus of many species all known for producing the psychoactive substance, psilocybin. When people talk about “shrooms” or “magic mushrooms,” they usually mean one of the Psilocybes, most commonly P. cubensis.
The Psilocybe mushrooms can produce uncomfortable—more rarely, even dangerous—side effects, but use seems to be relatively safe, at least in the short-term. Health effects of long-term use have not been studied. There is some evidence that psilocybin may have medicinal use, but again there has not been a lot of research. The experience of using Psilocybes varies a lot, in part because users themselves vary, but the concentration of psilocybin varies, too, between species and sometimes between mushrooms of the same species. Some strains are known for their visuals, others are known for their body high, and some are known for the clarity or insight they bring, or for some other quality—though whether these differences are real seems unclear.