First, proceed to Adafruit's Google Plus page here.
Next, locate the Show and Tell post. Add a comment to say you want to show off a project and we will add you to the "Show and Tell" circle.
We add you!
That's it! Once we see the comment, we add you!
Then, just look for the hangout announcement on the very same page later for your invite. There's an 8 to 10 (at the same time) people limit per hangout. If it's full, try later or just pop by next week at the same time. Some weeks are packed! At 7:30pm ET you will see a link to the hang out. Have your project ready to show and keep your microphone muted until we call on you.