Three quick steps on Google Play. Use the same Google account that's signed in to the Play Store on your phone.

1. 1Join the testers group
   Open the group
   Tap Join group. That's all you'll ever get from it.
2. 2Become a tester
   Open the beta page
   Tap Become a tester.
3. 3Install the app
   Get it on Google Play
   Says "not found"? Give it a few minutes after step 2, then try again.
4. 4Join your group
   Back to your invite