Authorize.net is one of the world's most respected payment processors. You will need to open an account with a third-party Authorize.net reseller - they do not sell directly to merchants. YOU MUST FIRST have a valid Secure Sockets Layer (SSL) certificate properly installed. Ask your web host to install this for you.
For additional assistance with Authorize.net AIM, see http://www.authorize.net/support/AIM_guide.pdf After SSL is installed, go to CONFIGURATION - Configuration - Shop Tab and make sure the "Enable SSL for sensible areas (recommended)" box is checked.
Login ID and Transaction Key
After you have been approved for an account by Authorize.net, get this information from your Account Information or Welcome Email.
You must have SSL installed and configured correctly for this to work.
Use Sandbox, Sandbox Login ID and Sandbox Transaction Key
Put your payment method into TEST MODE.
Start typing in the box for a list of credit cards to appear. Click each credit card name to select it, then repeat for multiple cards.
If you have uploaded a small image to display on payment methods, select it here.
OPTIONAL: CVV is Credit Card Verification Value, the 3-digit number usually on the back of your card. Select an image you have uploaded for the CVV Tooltip Help that shows the 3-digit number circled on the back of a credit card.