There are 2 ways to enable apache file and directory indexing.

Using Apache config file :

1. You can add directory options in the Apache configuration file directly. httpd.conf is a apache config file or you can add it in /etc/apache2/apache2.conf:
   
   

   # vi /etc/apache2/apache2.conf

<Directory /var/www/example.com/folder>

Options Indexes FollowSymLinks

</Directory>

2. Once you add the above code, save and close the file.
   
   
3. Restart httpd service.
   
   

   # /etc/init.d/httpd restart

Using .htaccess Files with Apache :

If you have .htaccess enabled, you can put a config line options indexes in your .htaccess file.

1. Open your .htaccess file.
   
   

   # vi .htaccess
   

2. Add the following apache directive.
   
   

   Options Indexes
   
   DirectoryIndex index.php index.html /example.php
   

3. Save and close your .htaccess file.