The Portal storyline (WARNING: MAJOR SPOILERS)

[robotpopcorn]

Before I begin, I need to say that I found this information from "PORTAL Unoffical Wiki"

Throughout the Portal series, you take on the role of Chell, a young woman trapped within the Aperture Science complex. Chell is forced to solve tests of varying difficulty in chambers designed by an AI-gone-rogue named GLaDOS. During the early stages of the testing, Chell is granted usage of the Handheld Portal Device (commonly referred to as the "portal gun"), a piece of equipment developed by Aperture Science that allows Chell to create portals that act as gates between each other, allowing Chell to quickly traverse areas or reach normally unreachable places.

Portal has two distinct parts, the test chambers and the escape.

Act 1: The Test Chambers
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The game begins with Chell awakening in a Relaxation Vault, where she is briefed by the voice of GLaDOS coming from speakers, before being released through a portal. The player is introduced to the testing process and mechanics, shortly thereafter obtaining the Aperture Science Handheld Portal Device. As Chell makes her way through test chambers, it becomes clear the facility is devoid of human life and GLaDOS is testing Chell for her own warped definition of 'science'. Throughout the facility are hidden "dens", containing mad scribblings from an unseen person warning others of GLaDOS. Motivated with the promise of cake at the end of the testing, Chell is put through tests of increasing complexity. When Chell is no longer of any use to GLaDOS, she attempts to kill Chell by lowering her into an incinerator. Quickly thinking, Chell escapes a fiery fate using the Handheld Portal Device, and she makes her way through the inner facility via maintenance shafts.
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Act 2: The Escape
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While Chell is making her way through the facility, GLaDOS attempts to lure her back with promises of cake and a party, and claims the attempted murder of the player was a misunderstanding. When she realizes her attempts are in vain, GLaDOS resorts to taunting Chell while continuing her efforts to kill her. Eventually Chell reaches GLaDOS' lair, where she finally comes face to face with the rogue AI. It is revealed that GLaDOS had murdered everyone in the facility using deadly neurotoxin. GLaDOS now attempts to do the same to Chell. Using the Portal Device, Chell defeats GLaDOS by removing her personality cores and depositing them in a nearby Emergency Intelligence Incinerator, resulting in a large explosion that blows a hole in the roof dragging both Chell and GLaDOS upwards. Chell awakens to find herself above ground in the parking lot of the facility, with the burning remains of GLaDOS surrounding her. The March 3, 2010 Patch modified the ending so that Chell is dragged back into the facility by the unseen Party Escort Bot.

The story continues with Portal 2, you can read the PORTAL Unoffical Wiki to read more.

https://theportalwiki.com/wiki/Story