From the Home screen, tap the the Google folder > Hangouts .
Tap the New icon to view the contacts from all of the Google Accounts you've added (at the top of the screen), followed by People you hangout with, and Other contacts (at the bottom of the screen).
Tap the name of the person in your contacts list.
OR
Tap the text field to enter a name, email, number, or circle.
Tap the text field (at the bottom of the screen) to enter your message.
Before you enter your message, you can tap the location icon (to the right of the message) to include your location. Tap the camera icon to attach a photo, attach a video, or take a picture (or video).
Tap the Send icon (on the right side of the message).
You can tap the call icon (at the top of the screen) to call the friend.