To play over Wi-Fi, you must first connect all devices in one network. This can be done in two ways: a) In one of the phone or tablet, go to the "Hotspoint settings". Enable access to Wi-Fi, then create a game on this device. In order to avoid the flow of Internet traffic on the device, which is an access point, switch off the mobile data. On other phones you want to connect to a given access point (by default called AndroidAP), this can be done via the "Wi-Fi settings". Then press the "Connect" in the "Wi-Fi game" menu, if everything is correct then you should see the server in the list. b) If there's an external Wi-Fi, you can connect all the phones to this point. Next to one of the devices to create a game, and at the other to connect.
The game has ads, but only in the main menu;-)