There are a number of CoPs on Discover:
https://community.naturephotographers.network/
https://forums.yoyoexpert.com/
https://intfiction.org/
https://forum.trustedhousesitters.com/
https://t-nation.com/
https://www.elitefourum.com/
https://community.cartalk.com/
https://forum.artofmemory.com/
https://forum.psaudio.com/ and the list goes on.
This is a traditional model. That text is assuming that the “practice” that people are coming together to discuss is the same for everyone in the group e.g. they are all there to discuss their interest in photography.
Can you explain why? What problem are you trying to solve?
The discobot tutorial and new user tips are designed to do most of this heavy lifting. Have you run through those tutorials as a new test user?
Creating test users in each of the groups and then impersonating them is the best way to do it. Or just create one test user in a different browser and change their permissions to reflect different groups.
There are a few community building communities out there. Read widely at feverbee.com and https://www.cmxhub.com/. There is also commchathq.slack.com (let me know if you want and invite).
See How To Find Your Community’s First Members | FeverBee. Generally they are already part of your “audience” elsewhere.