As with any other app, pokies apps can be installed through the App Store on iOS devices and the Play Store on Android devices. If you're using a casino's pokie app, you'll be prompted to sign in when you launch it for the first time, but afterwards you shouldn't need to do so again. Just make sure that if you want to play for free, select that option when you start up a pokie - you don't want to inadvertently spend your entire real money balance.