Firstly, if you're not using the app, set your phone's screen timeout to 15 minutes.
Then configure the phone you want to use as a controller. Pick "MASTER" from the starting screen, then enter your name and finally, pick the game you want to play. If you see a message that says "Your puppet has not connected yet", you're done.
Next, configure the puppet's phone. Pick "PUPPET" from the starting screen, then choose the name entered in the previous step.
Press some buttons on the controller phone and see if the puppet's phone displays those commands. If everything works, insert the phone to the mask/cardboard and make the puppet put on the mask.