Draw lines from those spots, which intersect with the corners of the perpendicular folds and run all the way to the edge of the paper.
Now we can begin using these creases to form the paper into a bag-like cube. It is helpful to do this with the short perpedicular fold flush against ...
Carefully hop in the bag with the rubber cement. Begin cementing all of the creases on the interior. Hold it there for a bit to let it dry
Fold top of the bag down to one side. This naturally collapses the bag and creates creases on the short ends.