Start by running the glue stick over the 3 edges on one side of the fold. Then fold the page on itself. Fold again perpendicular to last fold and .5" short of flush. Fold long end over short and glue.
Fold the bag in .5" on the long (closed) edges. Open the bag from top or bottom and flip the edge folds on themselves creating accordion folds.
What each side accordion fold should look like.
Fold the bottom, rough edge up 2".
Side view of folded bottom.
Lay bag flat and open the folded end portion. Pick a side and push the middle intersecting paper flat at its center most point. Then fold outer paper over inner smoothing ends to 45 degrees. Repeat
Picture of side folds.
Turn bag face away long ways. Fold top edge of bottom opening halfway down to bottom edge. Fold bottom over top and glue.
Final step gluing.