First, some Google Plus Hangout Basics, from the help files:
Hangouts can have a maximum of 10 participants. The easiest way to start a Hangout is to visit hangouts.google.com You’ll be taken to an invite screen where you can: Make sure you’re mic and camera are working correctly by looking at your video feed at the bottom of the page. You should be able to see yourself in the video feed, and when you talk, you should see a green bar appear at the bottom of your video. If you’re having issues with your mic or camera, try these troubleshooting steps. Invite entire circles or specific individuals to join you in your Hangout. Enable Hangouts on Air. Restrict people under the age of 18 from joining your Hangout by clicking Hangout Options and selecting the checkbox next to Restrict minors from joining this Hangout. Other Hangout participants won’t be able to invite minors and, the 18+ restriction cannot be changed once the Hangout has started.