Ginseng is a popular herb that is mainly used by older men in China to maintain there sexual stamina but it is much more than that.  In general, ginseng gives you more energy which can be directed toward sex, but can also be directed toward other things.  If you are finding yourself too tired or weak to do physical things, ginseng can help.  Many athletes take ginseng capsules or ginseng drinks to aid them in competition.  
    Serious scientific studies into the effects of this herb began in the 1960s.  A Russian study showed that soldiers that took ginseng ran faster than those who were given a placebo.  Dr. Brekhman, the man in charge of that study, was the first to refer to ginseng as an adaptogen, which is a substance that helps the body cope with stress.  A Japanese study using mice showed that the mice that took ginseng did tasks faster and with greater accuracy.  It sounds like a ginseng drink before taking exams would be a good idea.
A Japanese study also found that mice that took ginseng had less LDL (bad) cholesterol and more HDL (good) cholesterol than the ones that didn't get ginseng.  A study in India, also with rats, found that the rats fed ginseng could tolerate high altitudes and cold.
    Chinese healers have prescribed ginseng for high blood pressure, poor circulation, and heart disease for many centuries.  In general though, ginseng doesn't heal specific diseases so much as it gives the body more energy and greater balance allowing it to better fight off illness of any kind.
    One thing to note is that there is more than one kind of ginseng.  The ginseng grown in Korea is usually considered the best.  For a while, Siberian Ginseng was being promoter as being as good, but most herbalist now disagree.  American Ginseng ( P. quinquefolius L.) is a related, but different plant that has much of the same effects, but not as strong as Asian Ginseng ( Panax ginseng C.A. Meyer).