Ahhhh, Portal. The awesome, funny, yet creepy game. This game requires you to use your mind to solve puzzles. There are these rings called,"portals", and you must use these to win each level. Let me give you an example on how portals work.

-Say there is an orange portal on the wall.
-And a blue portal on the ceiling.
-If you go through the orange portal, you come out of the blue portal.

You recieve a portal gun, that shoots blue and orange portals.


While you are playing, there ia a robot called GladOs that monitors your progress. GladOs is obssesed with cake, and says hilarious quotes.

"Quit now, and cake will be served immediately."
"The Enrichment Center reminds you that the Weighted Companion Cube will never threaten to stab you and, in fact, cannot speak."
"I'd just like to point out that you were given every opportunity to succeed. There was even going to be a party for you. A big party that all your friends were invited to. I invited your best friend, the Companion Cube. Of course, he couldn't come, because you murdered him. All your other friends couldn't come either, because you don't have any other friends. Because of how unlikeable you are. It says so here in your personnel file: unlikeable. Liked by no one. A bitter, unlikeable loner whose passing shall not be mourned. "Shall not be mourned." That's exactly what it says. Very formal. Very official. It also says you were adopted. So that's funny too. "

In conclusion, this game is very well built, and you will lugh your way through.
Reference:
http://en.wikiquote.org/wiki/Portal