And you don't need Photoshop to use Layers. Just download the free, open-source GIMP editor and enjoy! GIMP can do most everything that Photoshop can and it doesn't cost you a dime.
Do you edit your digital photos using layers? If not, you're missing out on the single most powerful tool in your photo editing repertoire. Layers may seem baffling at first, but they're not hard to use—and they permit all sorts of powerful digital editing tricks.
You can use layers to combine photos, create double exposures, achieve special effects like selective color in a partly black-and-white image, and even correct a shot's exposure or color balance.[From Basic photo editing tricks with layers | Digital Photo | Digital Photo | Macworld]