Portal is a puzzle-solving game in first-person perspective. Its storyline is tied to Half-Life universe, with the introduction of Aperture Science, rival of Black Mesa, and owner of the Borealis, discovered in Half-Life 2 Episode 2 by Judith. You wake up in a test center but you don't see anybody although there are observations rooms. You'll be give the Portal Gun, which can create portals. Glados, the voice leading you from room to room, seems very interested in you. And she promised cake at the end...
Your goal is to find a way throughout the game for exiting each room without hurting you by using the Portal Gun, which can create two portals and help you to find a way if you can't advance. By using it, you can modify the way of an energy ball, make cubes going to impossible places or even make high and fast jumps by creating several portals when falling.
This game is also known as Half-Life: Portal in North America.