If you have SSL on your website (or want SSL), you have two options:
Option 1: If your SSL is on a separate subdomain, then you can easily use CloudFlare. All you have to do is designate the ‘SSL’ subdomain with a gray cloud in your DNS Settings page or on Step 3 of the setup process. This option is compatible with the FREE service.
Option 2: If your SSL is not on a separate subdomain and you do not wish to move your SSL to a separate subdomain, you will then need to upgrade to the Pro service. SSL support is free of charge to all Pro accounts on a per domain basis.
For more details visit http://www.cloudflare.com/plans.
Note: It will take 5-10 minutes for CloudFlare’s SSL to become active for your domain.