The best way: Buy the games. When you buy a game, they will ask you to sign up for an account. When you do, they will charge you for some game credits right up front, which you can use to buy the games you want. If you don't want to continue to be charged, make sure you delete your account after you have downloaded the games you bought. There's no penalty for doing this and you will keep your games. In addition, you can sign up again with the same information and it won't bother you about it.
