The light up cube inserts directly into the back of the Glo Pal character with the colored flat part of the light up cube being flush with the back of the character. To ensure air bubbles aren't trapped inside, please insert your character face down and head first into water. This will allow air to flow out of the small holes in the back of the Glo Pals character and allow water to activate the light up cube. Please see the video below for more directions.