SSL is basically the https:// thingy which means that the site is encrypted. You don't really need it for the whole site. Just the bit where CC information is passed to your host and to your gateway.
To get SSL you need to contact the host and ask them to install it. For now you can generate the key and certificate by yourself from cpanel then give those to the host. They will also need to assign a dedicated IP to the domain. Finally you need to buy a verified certificate from many providers and ask the host to change the certificate and you're set.
I used
Thawte and recommend them.