It was easier than I thought.
In the Amazon Alexa app, go to "Devices" and click on the "+" at the top right. Tap "Add Device" and choose "Camera". Select the brand of the camera and tap on "DISCOVER DEVICES".
That was easy.
I use it with my Ring Doorbell and my Wyze Cam.
Incidentally, since my Fire Tablet functions as an Echo, I can see these cameras on it as well.