We are planning to ride the sightseeing bus in Shanghai...

There are two lines such buses in the city: Puxi line (line 1)and Pudong line (line 2).
As for the specific information, you can search at the website:
https://www.travelchinaguide.com/cityguides/shanghai/transportation/sightseeing-bus.htm
Well, as for the ticket, at your boarding place, there is Ticketing Office, where you can get the ticket.