Monthly fee for iTunes

You don't have to pay for iTunes, but you have to pay for any content you purchase from the iTunes Store, the App Store (within the iTunes Store), and the iBooks Store (within the iTunes Store, in iTunes 10.3+). Also, if you've already purchased something on a different device using the same iTunes Store account, you can go to Purchased and download it for free.

In short, you pay for what you buy, unless you've already bought it.