Your game progress is saved automatically if your device is connected to the Internet. However, it may be lost if you reinstall the game.
In order to always be able to restore your progress, link your game to a social network account (Facebook / Google Play Games / Game Center / Game Circle). After you do this, you will always be able to load your game save if you sign in with the same social network account.
CAUTION! If you opt to reset your device to default manufacturer settings, you will only be able to load your game save if it was linked to a social network account. The same is relevant for transferring your account to another device. In this case it doesn't matter what platform device you were using before transferring.