Layer Masks in Photoshop Elements

Layer Masks are a very handy feature but are a little tricky in Elements. There are a number of ways to achieve them and there's even a Photoshop "action" that you can use to implement the feature fully (which I'll come onto).

Firstly what you're trying to do with a layer mask is to expose or hide chosen areas of another layer which sits above your background layer (or any other layer). For example I may have an image of my son which needs sharpening. I could duplicate this layer (ctrl-j) and sharpen this layer heavily. Then I could paint with a soft brush the areas I actually want to the sharpen using the layer mask (say his eyes). The handy thing is the mask gets saved with the image and you add or delete bits of the mask very easily.

Ok, the first method is to use an Adjustment Layer (AL). Duplicate your bottom layer and make the adjustments you want to this layer. Add any AL - say Hue/Sat above your bottom layer. And then select ok. You will the right thumbnail is the layer mask. This layer should sit between your bottom layer (or background layer) and the layer you have adjusted. Now hold the alt key and click in between the middle and top layer - you'll see the curser change. Now click on the right thumbnail of the adjustment layer. Draw black with the brush to cut through the top layer and show the bottom layer. Draw white to erase any strokes.

Second way is to add an transparent layer in between the two layers (instead of the adjustment layer). Group this the same way with the top modified layer. Now paint with black to expose the top (note this works the other way around to the true layer masks) layer and use the eraser to "paint white". This is the easiest method to use for my initial example.

Lastly download this action:
http://graphicssoft.about.com/od/pselements/p/layermasks.htm

Layer masks are also great for compositing / montages - whatever you want to call them. Probably easier using the free action for this. You can create a layer mask for each image to be montaged. Then either use the gradient tool or a soft brush to merge the pics together.
Another tip is if you only want to expose small areas of the top image using method 1 and three, is to fill the layer mask in black by setting the foreground colour black (D, then X until foreground black), then press Alt-Backspace. Now use the brush tool with the foreground black or eraser tool if using second method and paint the areas from the top image you want exposing. (This is great for sharpening selectively).