The game consists primarily of a series of puzzles that must be solved by teleporting the player's character and simple objects using the Aperture Science Handheld Portal Device (ASHPD, also dubbed the "portal gun"), a unit that can create inter-spatial portals between flat planes. The player character is challenged by an AI named GLaDOS to complete each puzzle in the Aperture Science Computer-Aided Enrichment Center using the portal gun with the promise of receiving cake when all the puzzles are completed.