If you would like to charge credit cards automatically once a day without manual intervention, you will need to enable the credit card capture task. Open the Task Scheduler window (under the Setup menu) and locate the task with the description "Charge credit cards of customers with pending invoices". Change the status for this task to Enabled and save the changes. You can also change the time at which the task runs in that window.
The Credit Card Configuration window contains an option named "Credit card capture when invoice due in (days)" which controls which invoices get charged each day. Configure the number of days before the due date of an invoice the customer's credit card should be charged.