IT is very simple,
This is how I use it
Adhere photo to a piece of paper, odd scrap works fine, you don't need a straight piecie of paper to mount it on. The top layer creates the lines (matte if the picture is cut on an angle all of your matts will be too)
Then you put the ruler that has a small little lip on top of the picture, butt it up to the picture. Then cut. Do this on all sides.
If you want to add anothe layer, adhere the matted piece to the next color, repeat!