Here's a clip from one of the videos to show what the pyramid boxes look like.
And here's the corresponding video with simple instructions. This one isn't in English (there are subtitles), but I included it because the instructions were the simplest of all the ones I watched. Plus, she discusses sizes, something others didn't.
Here's one that's even simpler, made in a different way. I love the fact that some of their examples are made from cereal boxes. These aren't quite as fancy, and tape is used to close them up (as opposed to the tie above), but they're simple enough that a child could make them with a bit of help from a grownup.
Finally, I'm including one more instructional video even though the instructions flew by a bit too fast for me. It's here primarily for the way she closed the top, so you can skip ahead to that part (around 1:35) if you like. She used a special punch to make the flower, but that looks like something I could produce on my own (or a different shape would probably work just as well. No reason it has to be a flower). With a simple square cut in the middle, she made a unique and cute closure. Interesting.
Enjoy! And have a wonderful day!