Cold showers have a myriad of benefits - everything from enhancing mood, to boosting your immunity, to promoting weight loss to improving longevity.
All that is required is that you...well...suck it up and do it. Anywhere from 2-5 minutes will do the trick. Turn the dial to cold and get in. You might prefer to get into a warm shower and then...when you get your resolve up...crank it to cold. Rotating your body helps. Make sure to breathe. Like anything...start with a little and build up. But keep it doable. It's best not to turn it into too big of an ordeal because you won't want to do it again.
Another good method is a contrast shower...alternating cold and hot water. An example would be alternating 20 seconds cold with 10 seconds warm...for several minutes. This really gets your circulation going.
But it's like anything...you really have to experience it to understand the benefits. It's not something to read about and analyze. It's something to do.
Give it a try. Besides having so many benefits, it's a good little test of will.