SSL certificate and HTTPS

Hi,
I've uploaded my website on my hosting.
I purchased a SSL certificate and it's already installed but it does not show the HTTPS in the address bar. I contacted my hosting and they told me that I have to update some php files like checkout page or shopping cart to be able to see the secure HTTPS.
Here is what my hosting says:

  You will likely have to edit some files to update your links. A shopping cart or similar install commonly has a configure.php file that contains the path to the certificate so that visitors are taken to a secure area once they enter the checkout. Pages will not automatically redirect or become secure unless you adjust the code/links or design of your site to use this.  

Question:
What page and code should I modify to be able to see the secure HTTPS ?
Thanks for any help.

I have written up a line of code that you can use to redirect to the https version of any page on your site. You would just add this code to the top of any of your checkout pages that you want to only be served via https. Here is a link to the post with the code:

showthread.php?p=48677&posted=1#post48677

Thanks Eric for the link.
I will insert it in my pages.