Whenever a player taps a snow land for mana, that player adds one mana of any type that land produced. That land doesn't untap during its controller's next untap step.
This has the supertype world. When a world permanent enters, any world permanents that were already on the battlefield are put into their owners' graveyards. This is a state-based action called the "world rule." The new world permanent stays on the battlefield. If two world permanents enter at the same time, they're both put into their owners' graveyards.