If your web site is offering a service or if you are selling any variety of products then you will, of course, need to be able to send invoices for goods or a bill for services rendered and to collect payment from your customers. While you do have a variety of methods for doing this, including setting up a merchant account and utilizing various methods to collect the billing information from your customers. You would then need to submit this information to the company where you hold the merchant account and then, they in turn, process the payment and finally you get paid. However, there is an easier way of getting paid by using a payment gateway.