Card processing is the final step to closing a sale. For this reason you want the experience to be as quick and easy as possible. Credit card forms take the total for all the items in your shopping cart and run them through a processor. While that part is simple, the processing fees may not be, depending on your credit and how many other third party services need to be used.
You can choose to accept card payments in the following ways: through your bank or a third party payment processor. The former involves a tougher approval process, but comes with minimal risk and a more stable experience. Using a third party is usually done if a bank denies your merchant services application, which is common for those with poor credit.