Then fold the three sides that are uncut, so the left, under and right side. The length between the edge of the envelope and the fold depends on how big you would like to have the bag, but I fold just about two centimeters from the edge of the envelope.
Then you open the envelope and you make it look like this picture, so the parts that you just folded are now the corners of the bag.
Then you fold the bottom of the bag into two triangles and paste or tape them just as you can see on the picture.
If you want to close the bag, just fold it trough the middle, just as I did at the first picture.



