5. Once you have folded all of the sides, tuck the flaps (squares) of the short sides in so that there are now 4 side walls to your box. Place a piece double-sided adhesive tape on the flaps. Remove the protective backing and then press the flap to the long side wall.
As an alternative, you may also use craft glue to adhere the box together. Craft glue takes longer to dry but holds a lot better. You can use paper clips or clothes pins to hold the walls together until the glue dries.