What is the difference between wood stain and varnish, and how do they each contribute to the overall finish of a wooden surface?

Wood stain is a colored liquid that penetrates into the wood to change or enhance its color, while varnish is a clear protective coating that sits on top of the wood to provide a glossy or matte finish and protect it from damage. Wood stain adds color and highlights the natural grain of the wood, while varnish adds a protective layer that enhances the appearance and durability of the wood surface.