About the game:

It's about going through a test chamber, where your only goal is the elevator at the end. Easy, eh? But it's not, as obstacles are well placed These obstacles canbe toxic water, energy balls, androids and maybe something else, too.
How to play:
First you need the Aperture Sciecne Handheld Portal Device (ASHPD). Tis device shoots a blue portal, which leads into an orange portal and vice-versa. Later in the game you will get your hands on the fully operational device, which can create an orange portal, too. Your guide in the game is GLaDOS (Genetical Lifeform and Disk Operating System), she gives you instructions via broadcasting. Portal keep forward momentum, so you can jump into one portal and rocket out the other portal, or as GLaDOS says ,Speedy thing goes in, speedy thing comes out.'.
You're Chell and you wake up in a mysterious building, where GLaDOS starts her speech. At first you learn the basic elements of the game, then you get the portal gun, which will be enhanced later in the game. That's about all I can tell, I don't wan't to spoil it for you.