I am following a High End Websites book and also the advice would be to put this:

<FilesMatch "\.(gif|jpg|js|css)$">
  ExpiresDefault "access plus 10 years"

Where will i place it anyway? I am using COdeIgniter. And That I get access to my httpd.conf file.

You really should place it inside your .htaccess file inside your site root.

Furthermore, Place the it within the <Directory></Directory> block inside your httpd.conf but it is most likely best inside your .htaccess for me.