The regular white glue is made out of polymers. These polymers are long strands that are either sticky or stretchy. Glue manufacturers have to find the right combination of sticky and stretchy polymers to make the best glue. White glue also contains water. Water acts like a solvent that keeps the glue liquid until you want it to stick. When you put glue on a piece of paper, the solvent water is exposed to air. The water eventually evaporate (Changes from liquid to gas). As the water evaporates, the glue dries out and hardens. All that's left is the sticky polymers that hold things to paper.