Hangouts is a full-featured messaging service from Google. It features instant messaging, telephone (VOIP), audio and video chats, either one-to-one or with a group, screen sharing and file transfer. It is straightforward and easy to use, and all you and the person(s) you're going to "hangout" (sonnect) with have to have it is a free Google+ account. Calling other countries will cost you a little bit (but much less than Skype, like 2¢ a minute to UK landlines) and calling any phone in the US, landline or mobile, is free!
If you're on a computer, open the Chrome browser (if you don't have it, go to our How to Download and Install a New Browser article), sign in with your Google account (your gmail address and password) and then grab the new Hangouts web app from the Chrome web store. If you haven't activated Google+, you should do it now -- you'll see the + button in the Chrome browser when you're signed in, or go to plus.google.com to sign up. Mobile platforms can find Google+ in their App store.
The one outlier is the Kindle Fire. Hangouts and Google+ are NOT available in the Amazon App store (nor are other Google apps), and you can't install it directly from Google Play. They can be "sideloaded" into a Kindle Fire HD and HDX, but if you don't have a computer and/or aren't comfortable following technical instructions, find someone (friend or child) who is and give them the link to the article below.