To create a secure connection to a page, first purchase and configure a secure certificate for your website. You can test if the certificate is installed correctly by hitting the admin site of your site https://MyDomain/admin. If you can connection, the certificate is installed correctly.
To set a single page to require a secure connection, edit the page and click the "Requires a secure connection" checkbox on the features page.
To make a template that requires a secure connection, edit it and check the "Requires a secure connection" checkbox.
If you have multiple domains on the site, and only one of them has a secure certificate, you have to create a secure template and use that template where needed. To do this, ignore the "Requires a secure connection" checkboxes and enter the secure link for the template in the template record.