They are all 100 by 100 pixels. I then denoted that each image be placed in the same space. I then denoted each image as a layer section in and of itself. Please note that the first layer you place is the bottom layer. They continue to go over top as you add layers.
NAME names the layer, obviously.
This won't come into play much in this tutorial, but will be important in later layer get-togethers. The LEFT is from the left of the screen to the upper left-hand corner of the image. The TOP is from the top of the screen to the upper left-hand corner of the image. The numbers are pixels. There will be a lot of playing with numbers to get the image exactly where you want it.