How do I obtain the 72 hour visa-free transit permit?

I will be staying in PVG for just under 24 hours and would like to go outside the airport and meet with some friends. My question is when I arrive at PVG, where do I go to obtain the 72 hour free transit permit? Or do I need to apply for the permit before I arrive at the airport? Is there a fee to obtain the permit? Does immigration service provide the permit?