Google Hangouts on Air events are view only events, you do not need a microphone or webcam to view the broadcast. If you work in a cubicle your co-workers might appreciate you using headphones.
Below is an example screen identifying the different sections of a Hangouts on Air Event and their purpose:
Once the Hangouts on Air begins you will see the live show. If you have a Google+ account you will be able to use the Q&A app to ask a question
You can also watch this video to learn more about participating in Google Hangouts on Air events.