visiting Forbidden town- transport from Capital Airport

Hello. Could you, please, advice what is the fastest and easiest way to get from Capital Airport to Forbidden town? I have only couple hours to visit the town, so can't be lost :) Is it better go directly by shuttle bus no.13 to Wangfujing Street or taking Express train and change to shuttle bus? Also how far is the entrance and exit from the stop for shuttle bus? Thank you for your help and advices, fully appreciated! Mirka from Slovakia