The portals are linked, making a tunnel that Chell can walk through. The tunnel works in both directions, so if Chell enters a blue portal, she will exit from an orange portal, and if she enters an orange portal, she will exit from a blue portal. The purpose of the portals is to make shortcuts to different areas, for example, if the player needs to get to a high ledge but is unable to jump to it, they can put a blue portal at their level and fire an orange portal above the ledge. Going through those portals will get the player onto the ledge.