How to create a layer mask in Elements

In Elements, a mask is only available with an adjustment layer.  Masks are useful to create effects and they are easily changed if the file is saved in *.psd format.

When first created and not altered in any way, the mask has no effect on its associated layer.  The mask layer thumbnail is white and  the mask layer can be "clipped" to any layer.

As an example, we can blend two layers together.

Move one image onto another as a new layer, activate the bottom layer and create an adjustment layer of any type so that it is between the two image layers and clip the top and the adjustment layer together.  Paint on the adjustment layer with black and where the mask is black, the bottom layer is revealed.  Grey  on the mask  gives partial transparency

Open the two images that you want to blend togrther

Click on one with the Move tool and shift+drag it onto the other.  This copies the first image onto the second as a centered new layer..

Activate the bottom laye and create a new adjustment layer.  It doesn't matter what sort but don't make any changes to it,

Alt+click on the junction between the top layer and the adjustment layer to "clip" them together

Activate the adjustment layer and paint with black / grey.  Where the mask is black, the layer below is revealed.

A gradient gives a soft transition.  "White reveals and black conceals" Try gradients of different width and different direction.