The old way to redirect all HTTP requests to HTTPS in the Apache configuration file...

RewriteEngine On
RewriteCond %{HTTPS} !on
RewriteRule (.*) https://%{HTTP_HOST}%{REQUEST_URI} [R=301,L]

But this method is no longer recommended (see "When not to use mod_rewrite") and this is the new way...

<VirtualHost *.80>
    ServerName www.example.com
    Redirect / https://www.example.com/
</VirtualHost>

<VirtualHost *.443>
    ServerName www.example.com
    # SSL configuration goes here...
</VirtualHost>