Addition to the merchant account you need a way to process the transactions on the Internet

From: radicalsoftware.com

Once if I have a Merchant Account Can I process E-commerce Transactions?

Your merchant account provider can tell you what the name of the processor are associated with your merchant account if you already have one, and whether your merchant account is able to process Internet credit card transactions. In order to send the payment to the processor, you need a payment gateway.