To buy songs or movies at iTunes Store, or to set up and use your iPhone, you'll need to create an iTunes account. To set one up, open iTunes and choose the iTunes Store option in the left-most menu. This will take you to the iTunes Store.
At the top right, you'll see a button that says Sign In. Click it.
Choose either “Create New Account” or enter you existing Apple or .Mac ID or AOL screename.
If you have an Apple ID or AOL screename, you’ll just need to enter your billing information and you’ll be able to proceed.
If you’re creating a new account, you’ll just have one more step. Choose your option and proceed.
If you’re creating a new iTunes account from scratch, the first screen you’ll see will ask you to agree to the iTunes Store's terms. Do so.
At the next screen, enter the email address you want to use for this account, to create a password and secret question, and decide if you want to sign up for any of Apple’s email newsletters.
The secret question can be anything you want, but be sure it’s something you’ll remember, since you’ll need it if you forget your account information.
When you’re done, click continue.
Next, enter the information for the way you want to pay for purchases at the iTunes Store. This can be a credit card, debit card, or PayPal account. Be sure to enter the billing address for your card and the security code from the back.
Congratulations! Now you’ve got an iTunes account and you’re ready to shop! Well, almost. There’s one more setting you should change.
To control how you buy things from the iTunes Store, you need to change a setting.
On a Mac, do this by going to the iTunes menu at the top right of the screen and choosing Preferences.
On a PC, go to the Edit menu and choose Preferences.
After you’ve done this, choose the Store tab. In that tab, the first options you have are to buy from the iTunes store using One-Click or a shopping cart.
One-Click shopping means that you’ll just click a “buy” button in the store and automatically be charged and download the song.
Shopping cart means that when you click the “buy” button, your purchase will be added to a shopping cart that you can review and edit before you check out and pay.
One-Click is more convenient, but it also charges you right away, so if you like to think about purchases or have an itchy trigger finger, you may want to choose the shopping cart.
Once you’ve made your selection click “OK” and you’re ready to shop!
This step is optional, but you should consider it. The iTunes Store has an offering called iTunes Plus, which allows you to buy higher-quality music, free of the restrictions of DRM, for the same price as regular music. Not all songs at the Store are available through iTunes Plus yet, but more are being added all the time.
If you think you might want to buy iTunes Plus music (and I can't think of any reason not to), follow these steps to enable iTunes Plus in your account.