Log into the site using your Apple ID (the same username and password you use in the iTunes stores), and Apple will display all of the computers they already know about.

一旦用你的苹果账户登录该网站(用户名和密码和iTunes商店的一样)，苹果就会显示他们所知道的所有电脑。

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From iTunes on your computer, open the Store menu, select "Turn on iTunes Match, " enter your Apple ID and password and click Subscribe.

WSJ: iTunes You Can Use

Once you set up iCloud using your Apple ID, any content that you buy from the iTunes Store will show up on other devices without any syncing.

WSJ: iTunes You Can Use

After all, in order to activate an iPhone, iPad, or iPod, you need to have an Apple ID and that means you need a credit card even if you only want to redeem an iTunes gift card.

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