I have made a number of these to make a gift card look like a mini present.
I can't remember the blog that I first saw them on, but I shall have to find it again and thank her, because the pattern has come in handy many times!
I will do my best to explain how it comes together, but I am hoping the photos will help.
You begin with a piece of double sided Designer Series paper that is 8" x 8". I was going to convert the design to metric, but the measurements are much easier in inches.
Begin by scoring
at 1.5", 4", and 6.5". Turn paper and score at 3" and 6.5".
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Fold in
each corner at right angles just shy of the score lines.
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Fold along 1.5" score line to the back.

With both 1.5" borders folded in, fold down the top 1.5" score line.
Fold the bottom up and tuck into the folded right angle corners.
If you fine that it is a little thick across the top you can open it up and snip out the top section and then refold.
It doesn't have to be a gift card. It can house little notes and promises of massages, doing the dishes, or the ironing or cooking. Or maybe they are my little wishes?!
Have a great day! We are at the moment, because it's raining!