1. There are two ways for a credit card / bank account to be saved to a customer account: via checkout on store front or through the admin panel
2. To save on the storefront, enable the payment method CIM / eCheck and proceed to checkout on your website
3. To save via the admin panel, either place an order for an existing customer and select ‘Save Card’ / ‘Save Account’ or go to Customers → Manage Customers → Select a Customer → Authorize.Net CIM (by IWD) and add the new credit card or bank account