A mask is an independent channel that can be converted to a selection outline and saved for later use.
The lesson this week involved selecting two images, creating a mask on one of the images, and inserting the masked image into the second image.
There seems to be several different ways to mask an image, but this week's assignment was to mask from scratch. This involved many steps that were sometimes very tedious, but the end result was amazing.
This is image #1 that was used to create the mask:
This is image #2 that was used as the background for the final image:
And, this is the final image:

