This codeigniter default htaccess file will remove index.php part from your web urls and also this will be a simple htaccess file which will only rewrite the urls. How ever to use this file mod-rewrite should be enabled form the Apache config file and this codeigniter default htaccess file will also minimize 404-errors from your website. So you should put this in to your root folder.
You also have to check the file permission in the folder.If your folder cannot read by the web user you will not able to see the rewrite changes and some times you might get errors. So before changing the file again and again please check the folder and file permission.
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