I am not able to use .htaccess file. Main problem is, I am not able to where to locate that

Comment posted to 301 Redirects and www/non-www Canonical Problems by Devesh

I am not able to use .htaccess file. Main problem is, I am not able to where to locate that file in my web application. I am using Tomcat 5.0 as webserver on windows machine. Anyone can please send me steps with directory structure to us .htaccess for www/non-www Canonical Redirection.