CodeIgniter PHP and .htaccess Help

I have a website built using CodeIgniter/PHP with a CMS and MySQL database. I need to add three pages of content to the site, rename three other pages and update the drop-down navigation menu file to display the new pages in the nav menu. I need help with making these updates. Each time I create a PHP file for the new pages using the PHP page templates specified in the theme folder, I receive a 404 error. This is a simple task for someone familiar with CodeIgniter and .htaccess files.