Decoupage

You can purchase Decoupage Solution or you can make your own decoupage glue:

To make your own decoupage medium, use equal amounts of white craft glue (Tacky Glue) and water. Squeeze some white craft glue into a small container or cup. Add water and mix until this reaches a milky consistency. Mixture should be paintable, but not too thick.

Decoupage, from the French word decouper, meaning to cut out, is the creative art of assembling, pasting and varnishing paper cutouts for  decorating objects.