A merchant account is a special type of bank account needed to process credit cards.
How do I accept credit cards?
To accept credit cards you must have a merchant account. To apply for a merchant account click the accept credit cards link on the main store manager page.
What is a payment gateway?
A gateway is a service that allows your site to process credit card transactions in real-time through your merchant account. You need a gateway if you want to have credit card orders authorized at the time your customer checks out of your store. A payment gateway manages the actual verification and processing of online credit card payments.
Configuring your payment gateway
Click the "store" tab at the top of the site editor.
Click the payment "Payment Methods/Merchant Account" link.
Choose your payment gateway and click the "set" button.
Enter the account information for your gateway.
Click the "Test" button to verify and save your changes.
Testing your gateway
To verify that your store is ready to real-time processing, go through your shopping cart and submit a test order.
Submit a test order through your site.
Login to your gateway (virtual terminal) to verify that the transaction shows up.