Gameplay
In Portal, the player controls the character, Chell, from a first person perspective as she is challenged to navigate through a series of rooms using the Aperture Science Handheld Portal Device ("portal gun"). The portal gun can create two distinct portal ends, orange and blue. Neither is specifically an entrance or exit; all objects that travel through the one portal will exit through the other with no change in momentum magnitude. If subsequent portal ends are created, the previously created portal of the same color is closed. Not all surfaces are able to accommodate a portal, and any attempt to do so will not affect the existing portals. Chell can also pick up objects, though she can only throw objects a short distance (affected by the player's momentum). These objects ("Aperture Science Weighted Storage Cubes" or a "Weighted Companion Cube") can be used to press large buttons to open doors or activate platforms, but barriers (known as "Material Emancipation Grids" or 'fizzlers', as described by the audio commentary) at the end of each test chamber or within certain test chambers prevent the player character from carrying such objects beyond them. Passage through these fields also closes any open portals, and portals cannot be fired through these fields
* source Wikipedia
