SSL stands for Secure Sockets Layer. It is a security measure for encrypting the link between the web server and the browser. Making the data passed through this link encrypted and in theory unreadable by snoopers. Most websites have SSL certification now days, the cart aspect of an online store certainly should if it does not i would advise not to shop there, anyone can getyour details with the knowledge.
Look in the address bar on your browser next to the domain/url. If there is a green padlock or the company’s name in green the site is secure! http://domain.com is not secure, whilst https://domain.com is! (notice SSL has an s after http).