American Green Card holder with Kenyan passport. Do I need a transfer permit?

I am a green card holder in America with a Kenyan passport. I will be traveling to Indonesia and have a 21 hr layover in China (CAN). Do I need an entry permit if I chose not to leave the airport? … I would however love to see a few sights while there, if possible, how do I apply for a short stay visa. I return 3 weeks later and have a 15hr layover. Would I need to get a month entry permit or and if so do I do that while still Stateside? Thank you!