From the article "Critical Components for e-Commerce on the Web" http://www.powerhomebiz.com/vol13/components.htm
Here's what you would need to open an online store and accept credit card payment:
1. Website - Your online connection to your prospects and customers. There are a number of places on the web to get "free" websites - although you may be required to display an advertisement. The design of your site is critical to the success of your business! If it does not look like a professional, legitimate business - NO ONE WILL ORDER ANYTHING - no matter how great the products you have. If you are serious about doing business on the web, either go back to school and learn html, java, cgi, etc., or hire a professional to design your site.
2. Merchant account - Bank authorized account which allows you to accept major credit cards, electronic checks, etc. Many banks will not give you a merchant account if you do business on the Internet because they may classify it as high risk. Be careful when looking for a merchant account provider! Watch out for hidden fees, high setup fees, and other unscrupulous business practices.
3. Payment Transaction Software - Software which actually processes customer order information, address, credit card number, etc. The data is sent to a credit card authorization network which verifies that the credit card is valid and verifies that the shipping address matches the billing address. A possible warning sign that the card has been stolen is that the billing and shipping addresses do not match.
Verisign Payflow services, for instance, costs as much as $59.95 per month for maximum of 1,000 transactions plus set up fee of $249.
4. Secure Server Connection - https:// - Link to a special computer which encrypts confidential ordering data for customer protection. You know you are on a secure server when the URL in your browser says "https://". The "s" stands for "secure." If ordering information is not sent via a secure server it can be intercepted by computer hackers.
SSL digital certificate to ensure secured transaction, which can set you back anywhere from $199 for two years with Thawte or $695 for two years with Verisign.
5. Shopping cart - Software which allows you to accept product orders for multiple products from your website. This software automatically calculates and totals orders for your customers. Some setup must be done in the html code of your website, and the shopping cart software must be installed on the server which hosts your site or on the secure server which accepts sensitive ordering information.
Read the article "Looking for a Shopping Cart" http://www.powerhomebiz.com/vol132/shoppingcart.htm
for tips on what to look out for when buying a shopping cart for your ecommerce business