Due to it’s popularity, it has got special attention from Google+ team. They have added 4 unique ways to start and use a Google+ hangouts across various Google products (as of this writing).
Four ways to start a Google+ hangout
Hangout from Google+ stream
This was the first method introduced that allowed to start / join a hangout. You’ll find this section just right of your Google+ stream. It also helps to find current live hangouts from your circle limited to a maximum of 3 live hangouts.
Hangout from YouTube
Hanging out from YouTube is a cool feature that allows to start a hangout right from any YouTube video and watch the video live with your friends or circles irrespective of wherever you are. You are basically on a virtual cinema theatre.
Really simple to use, goto YouTube, search for a video you are interested, click on the Share button and bottom right of the popup you’ll find a link to Start a Google+ Hangout (You must be logged in using your Google+ and YouTube account)
Hangout from Google+ Post
Hangout from a Google+ post was added just yesterday. It is a simple and easy way to connect with the post author through a 1:1 video discussion. You’ll be only able to start an hangout with the author only if you both exist in each others circle (mutual circles that is similar for Google+ chat).
Hangout from Google Chat
Hanging out right from Google chat in Gmail has been rolled out today. When you chat with someone in Gmail previously you use to see a Video icon. Now the Video icon is replaced with a Hangout icon and it allows to immediately start an hangout right from your Gmail.
Enjoy hanging out from Google+, YouTube or Gmail and have fun!