Fluxx is a card game in which the cards themselves determine the current rules of the game. At the start of the game, each player holds three cards and on a turn a player draws one card, then plays one card. By playing cards, you can put new rules into play that change numerous aspects of the game: how many cards to draw or play, how many cards you can hold in hand or keep on the table in front of you, and (most importantly) how to win the game.
What's in Nature Fluxx? Well, it has a whole food chain of woodland creatures from leaves to bears. It has frogs and snakes and trees and fish and spiders and rabbits and mice and mushrooms and worms. It has air and water and dirt, and it has the humans whose pollution can endanger such things. It has all the standard new rules and actions that make it Fluxx, plus a few new ones that go with the theme, including the Composting rule (which lets you draw from the bottom of the discard pile) and new types of "eating" goals (which let you win the game if your Keeper says it eats one of the other Keepers in play).