It's a breathing exercoise, used to quell sexual desire and libido. You stand up, hands on your knees which are slightly bent, and breathe deeply from the abdomen. (I think...)
Kind of like a kundalini yoga idea, it's supposed to transmute sexual energy into a sort of 'elixir of youth' within the body, reversing aging, etc...
Personally, I'd rather get a bit old and have had a good sex life!