Like any other time wasting game it runs on an energy system, and then you use energy to clear (dig) blocks to get materials/clear levels. Unlike other games it's kinda addictive and you can get decent bonuses (relatively) for watching Ads. Suddenly the amount of ads available to me has dropped to basically 0, the point where I can't get daily energy boosts let alone level/mission bonuses. Emailed support they said not their problem, they don't manage ads, and to try reinstalling.