Once you have added the SSL certificate to your website(s), if not then head over to read IIS 6: Add a Certificate to a Website to see how.
If you have a wildcard certificate, enabling HTTPS on port 443 for the multiple websites can be a bit tricky.
Modify IIS Metabase Directly (IIS 6)
To enable the edit-while running feature of the metabase by using IIS Manager
- In IIS Manager, right-click the local computer, and then click Properties
- Select the Enable Direct Metabase Edit check box, and then click OK
Editing the Metabase.xml
Open c:\windows\system32\inetserv\Metabase.xml, in a text editor. Search for your website Identifier in the ServerComment or website name in the ServerBindings
At the SecureBindings property enter between the quotes enter :443:example.com
If you have more websites, then repeat. Once you are done, save and close the file.
Open IIS Manager, expand Web Sites, and select www.example.com. Click on the Stop item and then Start item to make sure settings have been applied.