To transact credit card purchases online (while the customer waits), you need:

(1) A merchant account — that account enables you to transact credit card purchases via VISA, MasterCard, etc. (You need a business bank account in order to apply for a merchant account.)

Once you have a merchant account, you can usually "process" (put through) credit card orders via phone or, possibly, software that your merchant account provider provides.

The idea here is that, when a customer orders something — or you transact the order directly via your merchant account provider — the funds go directly into your bank account.

Note that this doesn't yet include your website. For that, you need two more things:

(2) A shopping cart — on the outside, a "shopping cart" looks like a bunch of ordinary web pages containing products and some type of "Add to Cart" button; select an item for purchase and you're taken to a page (or series of pages) where you input your name, address, credit card details, etc. If you've ever purchased anything online from Amazon.com, you were using Amazon's shopping cart. A very advanced and costly (in the millions) shopping cart, to be sure, but a shopping cart nonetheless.

On the inside, a shopping cart is a piece of Web software that allows you to add and delete products, set up categories, take orders, and sometimes other functionalities such as allowing you to print packing labels, email shipping information to customers, etc.

Note, however, that shopping carts don't just tie in to your merchant account on their own. That is, your shopping cart can collect order information, but you still have to process it somehow. To process orders online while the customer waits, you need a kind of online liaison between your shopping cart and your merchant account. That liaison is:

(3) A third party gateway — the outside company that performs the liaison between your shopping cart and merchant account. ("Third party" refers to the fact that the gateway company is not you/your website nor your merchant account provider, but an outside company.) This gateway is what ties your shopping cart and merchant account together, so that customer orders can be processed while they wait online. There are good, reliable third party gateways available — some of which also allow you to manually put through orders on their own websites.

There may be other things needed: assuming you're shipping goods and want to use USPS or UPS or FedEx, we can set up an accounts with either/both/all so that, when people order, their shipping costs are figured into the final amount they pay.

Lastly, it should be mention that some (or most) shopping carts are not at all search engine friendly and, unfortunately, it an generally said that many web design companies are not aware of search engine issues. This is a problem where you're relying on getting visitors from search engines in order to help with your marketing.