You have to pay the initial subscription period of 30 days online through Paypal, debit (iDeal) or credit card. Through this transaction you automatically give permission for the monthly direct debit to be taken from your bank account.
Payments are always taken 5-10 days prior to a new period of 30 days. Payment for your next month will be taken unless you have indicated, on time (at least 10 before the new period), that you do not want to renew your membership. A continuous failure of transactions will block your account until payments have been completed by you manually.