If a renter has entered a credit card for a booking, then all future payments can be deducted automatically from that card.
The other option is for the renter to receive an email notification with a link at the time the next payment is due, at which point the renter will be directed to make the payment manually (just pushing a button to charge the card).
The account setting for controlling whether payments are collected automatically can be found in Reservations > Settings. This will serve as the default for all your reservations.
The account setting can be overwritten per reservation. You can see where this control is managed per reservation in the Reservation Detail View (see #6).