Ok... I am really only assuming that origami is an ancient art. I learned how to do what I am going to do 1000 years ago it seems, so that is pretty ancient. I learned how to make the paper balloon on a school bus ride home from elementary school. An older girl taught me how to fold a torn sheet of notebook paper into an inflated box. She called it a paper balloon, so that is what I have always called it.
Start with a square piece of paper. In the pictures I am using colored computer paper, but it is a little thick. Origami paper (or notebook paper!) work better. Fold the paper in half, and then in half again.
Fold the top of each flap into a triangle. (First picture top row.) Tuck each folded down triangle into the opeinng on the sides. (That gaping opening in the first picture. The second picture is another few.
Almost done! I like to crease the top and bottom as shown by that faint line in the bottom row.
Crease everything very well one more time and gently blow into the hole at the top. It should look like this:
It should look like this:
You can do it! I learned it as a 5th grader!