Gmail users with active accounts can make free calls online through Google Chat. First, you must have Google Chat enabled on your computer or mobile device, and you must be logged in. To make a call, go to your Chat list and click on the phone link, then enter the phone number and select "call." The call recipient will either see your Google Voice number, if you have one, or a generic number if you don't.
You can also use the Gmail Hangouts app to make free calls online. The app can be used from a PC or a mobile device, including both iPhone and Android devices. Most calls from the United States and Canada are free when placed through Hangouts.
To make a call, open Hangouts and click on the phone link. Then search for a name or phone number, and select the name or phone number when it appears through the search function. If ypu are already in the midst of a chat with the person you wish to call, all you need to do is click the phone link at the top of the chat. If you also wish to receive incoming calls or texts, you must open a Google Voice account.