Merchant Account - otherwise known as a eCommerce Account; usually who you do your banking with.

Payment Gateway - the processing center for credit card transactions that send the $$ to your eCommerce account.

Secured Certificate - a certificate that is generated through the control panel and then signed by one of the few certificate authorities.

We at Video Integrations can put a complete eCommerce package together for you, or set up just the shopping cart; be it our custom cart that comes free with the Gold hosting plan, or the ShopSite packages we offer as an install on your server or as one of our several packages, you can read more about here. See eCommerce info