Go to www.steampowered.com , then Download the steam client, once installed, create a steam account. Then you log onto this when you open the client. There should be a store page. You click the game you want to buy, you might have to use the search feature and some games come in multipacks as well as singularly... then click purchase... you then follow through the payment details bits entering in your payment information, then you've bought it, its on your steam games list permanently, then it will automatically download the game. Then whenever you log into that account you will be able to play that game as long as its installed (steam installs while it downloads). And you never need to put in a CD for any game purchased on steam as the game is bound to that account.