Photomats: 
 the one on the left, the white layer is 4 1/4 by 6 1/4 so when you put a 4x6 photo you will have a small white boarder or mat all the way around the photo  -- this first layer does not have to be 4 1/4 by 6 1/4  -- it can be larger, 
but it can't be 4x6 or smaller
the next layer is black 4 3/8 by 6 3/8  -- this now meets the 2 layer requirement
the final layer is 5x7 and is not required
Also note that it is embellished, in the upper rt corner there is fiber and a brad and I also counted the zebra printed paper as an embellishement.
2nd photo mat (right side)
First, notice it co-ordinates but isn't exactly the same.  When I did my first swap I made my photomats match exactly.  Generally, most people make their mats coordinate ...but I don't know if that is a "rule"
Here the white layer is 4 1/4 by 6 1/4, the black layer is 4 3/4 by 6 3/4.  two layers.  I embellished with ribbon and brads  -- the photo is able to slip under the ribbon.   This is important to note  -- if the photo could not slip under the ribbon, then the whole thing would have to be bigger.
see in these photomats with the bugs--The top photomat the light green layer is 4 1/4 x 6 1/4, the next layer I made big enough to accomodate the bugs so that the photo could be added without cropping.  I think it is 4 1/2 by 6 3/4 or 7.   Notice the bottom photomat does not have 2 layers  -- this would not be something I turned in for a swap.
Tags:
I thik of it as one tag with a shadow  -- so two layers
in the zebra set--I started with a white tag with a black shadow.  I embellished it with the printed paper and the rub-on letters.  Finally--notice the hole  -- it must be filled in some way.  With fiber, ribbon, brad, eyelet and whatever else I haven't thought of.
Journal mats
the light green box is the writing area, then 2 mats brown and then green.  Embellished with the little plant and inked edges .
I hope this helps and that I haven't come accross as a know-it-all.