You don't. Its called a key, and if you don't have one in your possession when you need to open the handcuffs, than you really don't need to try picking one.
Okay, I unlocked this one. You can find the answer easily with a little search-fu on this site, but I am sure this will turn into another multi page "how to get out of handcuffs with your hands behind your body" thread as well..
