The area of payment processing can get a bit complicated, and it might be best to leave this to your web designer to sort out if possible. If you are able to use one of the payment processing companies that are already supported by Ecommerce, it will make life a lot easier (you will need to sign-up with a payment processor yourself - the program won't do that for you!). You can see the options available by clicking on the List Payment Methods icon on the store summary, or by selecting List Payment Methods from the Store menu.