I wasted two days trying to learn Hangout and just replaced it with
8SMS . Other people like Textra better than 8SMS. Everytime I tired to send a SMS with Hangout it became a email. There are a lot of people using Hangout but the UI is very strange when all you want to do is text someone. I still can't use Hangout. I would say download 8SMS or Textra from the Play Store then go to setting>More>default SMS and change it to either Messaging (8SMS) or Textra.
I wanted a SMS/MMS text App not a iMessanger, Facetime, Facebook with SMS and MMS App like I think Hangout is trying to become the total communication App.