You should be receiving monthly statements for your credit card, either in paper form or electronically via your online banking system. Each statement will have a list of transaction processed in the billing cycle it covers, the total amount you owe, and the payment due date. You can use this information to determine how much you must pay and by when.
Note that the due date indicates when the payment must be received by the issuer of the card. If your credit card is issued by a bank different from the one you use to make the payment, allow at least three working days, or five, to be safe, for the payment to be processed by both the paying bank and the credit card issuer.
Even if you set up automatic payments, you do want to review each statement to ensure there are no fraudulent or unexpected charges. In most cases, if you don't dispute the wrongly charged amount before your next statement, you'll lose the opportunity.
Note that your bank does not guarantee that you receive the statement each month, only that it makes its best effort to send it. Depending on the level of trust you put in the statement delivery method, you may want to also track your credit card charges and the due date separately, as explained in the other answer, or at least contact the bank if you don't receive the statement on the expected day of the month.