Hummm. I clicked, "Groups", but do not see the, "Join" button...
You must go to the particular Group, and on the particular Group's main page you will see a Join button.
Once you have joined a certain group, you can post in it and see all the replies to any threads there. If you want to 'unjoin' a group, you just click the same button again, it will say "leave group" if you are a group member.
Let me know if that works for you! :)
Those irritated by grain of sand best avoid beach.
-Strumelia proverb c.1990
updated by @strumelia: 03/04/21 08:33:40AM