Basically SSL stands for Secure Socket Layer, and if you have been around for long enough, you would know that the first advent of this technology was actually perpetuated by this little known browser called Netscape. Well, Netscape is not around anymore, but their technology has definitely stared and has evolved to something that has overcome the commercial aspect of online transaction all over the internet.
When you buy something on the internet, you would have seen some sort of SSL tag on the payment page, which means that the website has a certificate that would give you the piece of mind that your credit card details and your personal information is safe and secure. Now, plenty of websites that deal with buying and selling have this certificate as standard and it has been recognised as one of the premier ways of securing online transactions. How it works is that there is a Certificate Authority that is a third party protocol, which works sort of like a merchant on both ends of the transaction. What happens is that the information is identified on both ends and decrypted, passing through secure channels of the credit card merchant and the website selling the goods in the first place.
The system works in this way, firstly when the transaction goes through, the website that sends the information will request for a secure page to continue the transaction. It will then send the public key with the SSL certificate, where the browser will then check for its authenticity and the source against a list of key trusted certificate holders. On both ends of the transaction, there is random encryption of the data sent, which is layers of security that helps to protect alot of potentially sensitive data. A bit of literature on the encryption is that it uses a key system, pairing together a public and private key to ensure that the data can be randomised and encrypted by one set of keys and reversed only by the other set. This is sort of like how one lock can open a door and only another lock can lock it.
The system may seem cumbersome but in the realm of the internet and transactions online, this is very necessary and it works. This way, the server and the merchant bank (VISA< MASTERCARD, AMEX etc) can then trace where the problem (if there is one) or where the leak in security occurs. The certificate is the second layer of security, which allows you to know exactly who you are dealing with and that the person you are sending the money to is the person that you are dealing with. A certificate can only be issued in a transaction if its signed, which will then allow the data to be sent to the correct people. This is the nature of the SSL Certificate and this system of security keys and layers is why you must always trust websites that have this certificate when giving up data like credit card numbers.