Webopedia defines SSL as:
“SSL (pronounced as separate letters) Short for Secure Sockets Layer, a protocol developed by Netscape for transmitting private documents via the Internet. SSL uses a cryptographic system that uses two keys to encrypt data − a public key known to everyone and a private or secret key known only to the recipient of the message. Both Netscape Navigator and Internet Explorer support SSL, and many Web sites use the protocol to obtain confidential user information, such as credit card numbers. By convention, URLs that require an SSL connection start with https: instead of http:.
Another protocol for transmitting data securely over the World Wide Web is Secure HTTP (S-HTTP). Whereas SSL creates a secure connection between a client and a server, over which any amount of data can be sent securely, S-HTTP is designed to transmit individual messages securely. SSL and S-HTTP, therefore, can be seen as complementary rather than competing technologies. Both protocols have been approved by the Internet Engineering Task Force (IETF) as a standard.”
All you need to know is that to securely do business over the Internet, you must have SSL capability for your website. If the web host plan you are considering does not support it, then look elsewhere.
Also, keep in mind that if you use the standard PayPal shopping cart, that SSL is provided at no additional charge, however, if you are interfacing to PayPal through another shopping cart or merchant account service, then SSL capability will need to be considered.