Gather a rectangular sheet of paper
Place the paper flat with the longer side horizontal
Fold one side edge inward about 1 to 2 inches
Apply glue or tape to the folded edge
Roll the paper into a tube and seal the edge
Press the tube flat
Fold up the bottom edge about 2 to 3 inches
Open the folded bottom and flatten the corners into triangles
Fold the top and bottom flaps of the base toward the center
Tape or glue the base closed
Open the bag from the top
Fold the top edge down if desired for reinforcement