The first step to using Google Hangouts with your iOS device is to install Google Hangouts from the App store or from this link.
After you’ve installed and opened the Google Hangouts app you should see a page similar to the one below-left. If you haven’t signed in with a Google account you will see a page like the one below-right. If so, sign in with a Google account (@gmail.com) to continue.
Once you are signed in, tap the plus button on the bottom right of your screen. Doing so will show a screen like the one below:
From here you can add your teammates by entering the Gmail account they used to sign into Hangouts. Once your group is set up you will be able to have a group chat/call with all members of your group.
If you are going to use Google Hangouts to communicate and coordinate tactics during a match, please set up your Google Hangouts beforehand to ensure you have the most gaming time possible!