Authorize.net is your payment gateway.
A payment gateway is a service that allows accepting credit cards over the Internet. A payment gateway does for a website what a swipe terminal does for a physical store like a Wal-Mart: it encrypts the credit card data and sends it out securely over the payment network. Your 4aGoodCause pages will communicate with the payment gateway to process credit cards online.
Each time a donor submits a donation on your 4aGoodCause page we securely pass their card information to Authorize.net for processing. Authorize.net will "virtually" swipe the card. If the card is accepted then a transaction ID and approval is sent back to the donation page.
Each day Authorize.net will batch transactions received that day and send them to your merchant account for deposit.