How can I enable clean URLs?
The settings for the clean URLs are at admin/config/search/clean-urls.
That page shows the "Enable clean URLs" checkbox only when it is possible to enable them; when the server is not configured to support them, that page shows the following message:


  Clean URLs cannot be enabled. If you are directed to this page or to a Page not found (404) error after testing for clean URLs, see the online handbook.


On an Apache server, and with the default settings used from Drupal, clean URLs work if:


The mod_rewrite module is enabled for the server 
The following directives are present in the Apache configuration file 

AllowOverride All
AccessFileName .htaccess