You will be charged via your iTunes account. The charge will be billed automatically every month.
$4.99 per month. Prices subject to change. Premium membership subscription is automatically renewed each month from the date of initial purchase.
Details of auto renewal
Subscription auto-renewal must be canceled at least 24 hours before your renewal date. If you cancel less than 24 hours before your renewal date, your cancellation will take effect the following month and subscription stopped.
How to cancel auto renewal
You can cancel your premium membership subscription by turning off auto-renewal in iTunes/Apple ID settings. You can confirm that the subscription has stopped by checking your iTunes/Apple ID settings after the next renewal period has passed.