You will be billed every 30 days, beginning with the date of your initial payment.
If you purchased an annual subscription, you will be billed 365 days from the initial purchase date. If you purchased the Black Friday promotion, your next year will be full price.
Note, this does not mean once a month, it means every 30 days (sorry, we know this part is slightly confusing). This means that in some cases, it is possible to be billed twice in one calendar month. For example, a person who signed up February 29th on a leap year will be charged twice in March the following year.