Meaning: This sentence is describing the appearance of the snow, comparing it to cotton to emphasize its whiteness and fluffiness.
Choice of Words: The word "white" describes the color of the snow, which is the absence of any color. "Fluffy" means soft and light, like a cloud. "Cotton" is a soft, white material made from the fibers of the cotton plant. When you put these words together, you get a vivid image of the snow as being pure white, soft, and fluffy, just like cotton.