Your achievements and stats can be viewed in Steam under: "Community -> My profile -> View all my games -> Portal (view stats)"

Achievement	How to unlock
Aperture Science	Earn gold medals on all Portal challenges.
Basic Science	Earn bronze medals on all Portal challenges.
Camera Shy	Detach security cameras from the walls.
Cupcake	Beat two Portal advanced maps.
Fratricide	Do whatever it takes to survive
Friendly Fire	Knock down a turret with another turret.
Fruitcake	Beat four Portal advanced maps.
Lab Rat	Acquire the fully powered Aperture Science Handheld Portal Device.
Long Jump	Jump 300 feet
Partygoer	Make the correct party escort submission position decision
Rocket Science	Earn silver medals on all Portal challenges.
Terminal Velocity	Fall 30,000 feet.
Vanilla Crazy Cake	Beat six Portal advanced maps.