how much is the shuttle bus, and what are it's stops?

There are many shuttle bus lines in Beijing and their stops are different. You can see details on this page:
https://www.travelchinaguide.com/cityguides/beijing/transportation/airport-shuttle.htm
https://www.travelchinaguide.com/cityguides/beijing/daxing-airport-shuttle-bus.htm

Also, the Great Wall is so long and there are many sections can be visited.The most famous sections are Mutianyu and Badaling Great Wall in Beijing, and you can take a direct bus at Qianmen. To Badaling, you can also take bus no. 877 at Deshengmen Bus Terminal; or take high speed train at Qinghe Railway Station.