You can see who is in your group once you join one. Once you’re in, you can press the "Discussions" tab at the top of your screen to start a group chat with everyone in your group.
Then you can (and should!) select a group gathering you can attend. Once you’re RSVP’d, you can view comments about that gathering. Here you can say “Hi!” to fellow attendees and dive into discussions. Then continue those conversations in person at the gathering!