Do I actually have to buy anything ?

Nope, download and install iTunes and use it to go to the store on tuesdays. They are supposed to have a new song up every week starting next tuesday. They are actually doing a free song everyday this week (today's is a Courtney Love track). You do have to setup an account which requires a US address and you might have to give them a credit card number (they already had mine so I'm not sure), but you don't have to buy anything to get the free song.

-Mike