To add a recurrent bill, go to Bills and click Add Bill.

In the add bill form, fill in the description with a text that identifies the bill for you, the category the bill will be associated to by default, the amount and currency, the default account the payment will be made from and optionally any notes; Pro accounts can also choose to attach documents. For the recurrence part, select the "Yes, it is a recurrent bill" and set its frequency and issuing date, as well as the due date and the date of the first invoice.