Operation: New Earth can connect to Game Center, Google Play Games (depending on your platform), and Facebook. If you connect to Facebook then you can continue your game between both iOS and Android platforms.
On the device with the account you'd like to continue, access the Settings menu from your base map by tapping the gear icon near the bottom right of the screen.
Next, choose either Game Center, Google Play Games, or Facebook.Once you've opened the Settings menu, tap the Account button.
Your game will now be connected to that service.
On your second device, install the game and play through the opening tutorial. Once you can access the Settings menu, repeat the above steps and then chose the same service that you chose before and you'll receive a new prompt asking which account you would like to use with this service. Simply choose your original account and tap Use Player to link that account to your new device!