Monkey Masking Tutorial Page 2
Step 4
Now you are ready to begin the fun!! Click on the Monkey Layer in your 'Layers Palette'. Then while still in your 'Layers Palette', go to the 'Opacity' box at the top and lower the Monkey layer's opacity to approx 65%. This is just a temporary step to enable you to see below to your People layer, so that you can line up the head and eyes into the correct position. Once you've done this, you will again return the Opacity back to 100%.

Step 5
After you've lowered the opacity, go to the Main Menu, choose 'Edit', 'Transform', 'Scale', in order to resize the Monkey head to approximately the same size as the person's face that you wish to cover. Then before you press 'Enter' to save your resize, go to your Main Menu again and choose 'Edit', 'Transform', 'Rotate' in order to turn your Monkey face to the same angle as face you are covering.
Important Tip
Do all your 'Scaling', 'Rotating', 'Skewing', etc., all at once. Only press 'enter' to save your choices once all of them are complete because each time you make one of these changes, you are diminishing the resolution of your Monkey image. If you scale and rotate all in one sequence, and press enter only once ( as opposed to pressing enter after scaling, then again after rotating, etc.) you will only be losing resolution once, instead of multiple times.
Now you may once again raise the Opacity of the Monkey face back up to 100%. After you've done this, go to the bottom of the 'Layers Palette' and click on the round circle (where the red arrow is pointing in the picture below). This creates a Layer Mask on your Monkey layer, which will allow you to 'paint away' the unwanted portions of that image.