There are loads of videos on YouTube with step by step on folding to make
the box. I just did a search on Google for origami boxes.
What we did was to separate the front from the back of the card and then you
need to make each piece a square. Do this by folding up one corner to meet
the other side...then trimming the excess so you have a square. Is this
"clear as mud"?
Then trace around this on the back side of the card...but then you need to
trim off about 1/4 inch or so from two sides on this piece so the bottom box
will be small enough to fit inside the top box.
This will give you the two squares with the back side a wee bit smaller than
the front.