Begin by cutting three pieces of cardstock, 4 inches x 4 inches. I have used two pieces of card the same colour and one of a different colour so that you can see the positioning clearly later.
Position the pieces as shown above and tape down all the areas where two pieces of card meet. Tucking the last piece inside so that it creates a pyramid shape. The picture below shows the final result. Decorate as desired. When you have the finished piece, fold one of the back sections in half so that it will fold flat, this will then fit into a standard C6 envelope. Obviously, the size of cardstock can be adapted to fit any size envelope as long as the original pieces you cut are sqaure.
I hope that you found this tutorial fun and simple to make. This is not my creation and therefore you can find other methods on the internet if you wish. However you decide to make it, have fun!