If you’re using Google Chrome, I recommend downloading the Google Hangouts extension (https://goo.gl/JXPtm). This places a button at the top of your window that will allow you to start a Hangout. It will also listen for an invitation to Hangouts and open the conversation window. As this is a Chrome extension, Chrome must be running for this to work.
Here’s a quick video (https://goo.gl/mUoIQq) that explains the installation process and what you can do with it. Although I didn't mention it in the video, you can also use Hangouts to make free calls to phone numbers in Canada and the United States.
For information on Hangouts visit Google’s Help Centre: https://goo.gl/0p3Uzw.