HTTPS can be a valuable tool for securing your website. It operates much the same way as standard HTTP, with an added SSL/TLS encryption layer. This serves to create a secure means of communication over the inherently insecure internet.
It can be quite expensive to get a suitable certification - some companies do offer cheaper certificates, which simply verify that a domain exists. These are not generally considered to be of much worth by the security community (although an end-user is unlikely to notice or care).