Htaccess files are used in apache using the .htaccess extension, it has no file name, and if you can't see it, you may need to play with your Folder Options in windows or your FTP client. These config files for apache are extremely useful to prevent access and to rewrite urls using mod_rewrite so that they are more search engine friendly and optimized. Some tips and tricks for designing the right .htaccess file for your website can make wonders.