When you visit sites such as PayPal, AlertPay, or other sites that partake in the transfer of personal details, you notice that http:// changes to https:// and a "verified" bubble appears in your address bar. This confirms that the site is who they claim to be.
SSL in general just means that you are connected to the server in encrypted format. Your ISP is unable to view what is being sent to and from the server, just that you have connected. It's this reason many banking and VPN services use SSL.
