how can i play mw2 online?

i just downloaded mw2 to my pc how can i play online?

buy the game
/end of story

hahaha...What a happy ending xD

If you bought Call of Duty: Modern Warfare 2 off of steam, then you should of downloaded both the games that came with your purchase. Download "Call of Duty Modern Warfare 2 - Multiplayer" and start it up and you will be directed.

If you bought it on CD, then you should be able to start up the game itself and play Multiplayer from the menu.

Correct me if I am wrong, because I have never bought it by CD.

IF you buy the game it should install, then you validate with Steam that you bought it with a special key in the game case, then once it's done you should be able to play fine. Sometimes you'll have to right click on the game in the Game tab, go to properties, then validate the files.

If you've downloaded a pirated version check for private servers online like Garena