I was also wondering how to use this plugin, and I'm posting this in case you(or anyone else for that matter) has not already found the answer.
Basically, I had never used the custom fields before when editing a page, and as of 3.1 I believe, the custom fields on the edit page are hidden by default. The installation instructions should be a bit moer clear and say that you need to add a custom field on the edit page, rather then editing the page and adding your own meta data tags(which it appears you attempted to do, and I also assumed was what was needed!)
To add a custom field on your edit page, first un-hide them by clicking on "Screen Options" up in the top right hand corner of the edit screen. Next, check the box that says "Custom Fields"
After you have checked that box, a new section will appear on your edit screen towards the bottom called "Custom Fields"
In the "Name" section on the left, enter "force_ssl" and in the "Value" section on the right, enter "true" then update your page and you're all set!
I hope this helps save someone some time!