Redirect to https via .htaccess

RewriteEngine on
RewriteCond %{SERVER_PORT} !^443$
RewriteRule ^.*$ https://%{SERVER_NAME}%{REQUEST_URI} [L,R=301]

The [L] flag causes mod_rewrite to stop processing the rule set. The [R] flag issues an HTTP redirect to the browser (301 stands for Permanent Redirect). This depends on mod_rewrite module.

For a complete reference head over to apache docs.