mjpg_streamer, Octopi, Kubuntu
Going to post the answer here for posterity and for those, like me, trying to cope with Linux after making a career in Windows.

I'm running Kubuntu 18 because I didn't want to have to buy an operating system or install a bootleg copy of Windows. The most important thing for a Windows user to know is that the readme.md file is important. Think of it as a .chm file, or a series of linked help documents. What you want to know is THERE, not on the github page. 

Using the following command in the mjpg-streamer-experimental directory got me where I needed to go.

mjpg_streamer -i 'input_uvc.so -d /dev/video0 -r SVGA -f 30' -o 'output_http.so'


e.g. webcam, 800x600, 30fps to http (port 8080 is the default) The MD files break it down. I also found two web pages very useful: 

http://skillfulness.blogspot.com/2010/03/mjpg-streamer-documentation.html
https://wiki.ubuntuusers.de/MJPG-Streamer/

In OctoPrint the streaming setting is then:

http://127.0.0.1:8080/?action=stream


In my case, I use the network IP rather than local host so I can monitor the print from my upstairs PC. For snapshots: 

http://127.0.0.1:8080/?action=snapshot


I'll admit that Octolapse doesn't work for me yet because I'm still trying to work out ffmpeg, but that's another issue. EDIT: got that done, too. Useful command: 

whereis ffmpeg