The app then walked me through it. I selected 2nd Gen motion sensor, then pulled the plastic tab out of the battery compartment, and the sensor found the network, and all I had to do was name it, stick it to the wall, and run a test to make sure it was sensing motion. It arrives out of the box with its sensitivity set to maximum.
https://www.amazon.com/Ring-Alarm-Motion-Detector/dp/B07ZB2QF2V