I want to use Cache Control and ETag in my joomla website as suggested by google. But have no idea how to do that. I googled it a lot but could not find any worty example.
Can anybody tell me how to do that..??
For Cache Control i have found this example, but is this the complete syntax..?? and where to place it in <head> tag of the index.php file??.
Also please tell me the syntax of ETag and the place where to write it.
You can use your .htaccess file at the root of your website for this. You'll find lots of variations on the specifics, here's a comprehensive one from http://www.siteground.com/tutorials/joomla/joomla-speed.htm#htaccess.
Using a text editor, add the following to your .htaccess file
EDIT If your goal is specifically to improve your YSlow score and you aren't using these tags for any other purpose, it may be better to set the ETag below to:
Source: https://developer.yahoo.com/performance/rules.html#etags
Alternatively, you will find plenty of extensions which will do a similar thing in the JED
http://extensions.joomla.org/extensions/core-enhancements/performance/cache
Good luck!