Maybe it's much easier than you think. If your provider has installed the certificate, then just call the page with the correct protocoll, that means https://www.example.com/page.html
instead of http://www.example.com/page.html
.
The difficult part is to make sure, that the page can only be called with the HTTPS protocoll and is not accessible with HTTP. Relative links will use the same protocoll as the originating page.
The easiest way is surely, to make your whole site HTTPS only (you can use relative links then). Some providers offer this option in their control panel. If there is no such option, you can write a .htaccess file and place it in the root direcotry. This lines will redirect any HTTP requests to HTTPS requests:
RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https://www.example.com/$1 [R=301,L]
Of course you should replace example.com with your own domain.