Probably one of the most used payment options (gateways) within Magento, and most likely every other cart system is the PayPal. This payment gateway is built into the default Magento installation. All you need to do is to punch in few configuration options under “System > Configuration > Payment methods“ and you are ready to go.
Great thing about the PayPal – Magento relation is the IPN feature of the PayPal itself. By definition IPN stands for Instant Payment Notification. Its a feature of PayPal that allows you to integrate your PayPal payments with your website’s back-end operations, so you get immediate notification and authentication of the PayPal payments you receive.