what is .htaccess file and for which purpose it is used? what functionality can i do with .htaccess file?
htaccess files can give you extra control over your server, allowing you to password protect directories, enable server side includes, generate custom error messages, and block users by IP address among other things.
Google is your friend - http://www.google.co.uk/search?q=htaccess there is also extensive documentation and examples on the official apache website: http://httpd.apache.org/docs/1.3/howto/htaccess.html