If you click on the photos they will appear bigger.
Start with a 12" x 12" piece of cardstock and cut it in half to give you 2 pieces 6" x 12". You might be best trying this out on some scrap card first just to get the feel of things.
Measure 3" (on the 6" edge) and cut from the 3" mark to the opposite side giving you a shape like this.
Do this on both pieces.
Now score at 4" and 8" on both pieces.
Cut half way up from the bottom at 2" and 10" on one piece and down half way at 6" of card and on the other piece, cut down at 2" and 10" and up at 6".
This picture might explain things better.
Fold on the score lines.
Now slot the bottom 2" cut in to the top 2" cut like this.
The slot the bottom 6" cut into the top 6" cut
and now for the tricky bit, slot the 10" bottom cut into the top 10" cut and there you have it.
Decorate as desired.
I would suggest that if you are going to decorate similar to mine by using layers of card, you might want to measure these up and get them all prepared before you assemble the card but stick them down after you have put the card together.
I haven't taken very good photos but I have a layer of grey card and then the patterned on top.
Any questions, please ask. I'm not the best person in the world for explaining things Lol!