From Beijing Airport to Sacred Way? And from there to Yinshan Pagoda Forest?

To the tombs and Sacred Way: take airport shuttle bus line 4 to Madian Bridge. Then, change to bus line 872 to Dagongmen Station, and walk north to the place.

To Yinshan Pagoda Forest: take bus line 314 from Dagongmen Station to Changping Dongguan Station. Then, change to bus line Chang 31 to Humencun Station, and walk north to the pagoda forest. :)

Personally, it is complicated and time-consuming to travel by public transportation. You may consider renting a taxi or private car for a trip and the driver will wait for you during visit. The total fare can be CNY500-600 or around.