What are the differences between wood stain and varnish, and how do they affect the appearance and durability of wood surfaces?

Wood stain is a colored liquid that penetrates into the wood to change its color, while varnish is a clear protective coating that sits on top of the wood. Stain affects the appearance by changing the color of the wood, while varnish enhances the natural beauty and provides protection against wear and tear. Varnish adds durability by creating a barrier against moisture, scratches, and UV rays, while stain primarily affects the color and does not provide as much protection.