 The initial tutorial levels guide the player through the general movement controls and illustrate how to interact with the environment . The player must solve puzzles using the ' portal gun ' or ' Aperture Science Handheld Portal Device ' , which can create two portals connecting two distant surfaces depicted as matte white , continuous , and flat . Characters can use these portals to move between rooms or to " fling " objects or themselves across a distance . Outlines of placed portals are visible through walls and other obstacles for easy location . 
