Need Help Creating Registration/Login Form

I know it's accessing index.php (which right now is just whatever Code Igniter has for it as code by default) because the "Index File" config is set to : $config['index_page'] = 'index.php';

I'm assuming I would change that to the home page of my site (after the successful registration), correct?

Either way, I don't know what the User/register is at the end of that address. But that's probably what's causing the 404 error now.

index_page is your the name of your index file (default is index.php), but can be empty if you configured "url rewrite". This never changes once you started using the framework.

What goes after index.php is usually the page that is being requested in the format /index.php/CONTROLLER_NAME/METHOD_NAME/
In your case you have "User" controller and "register" method (or at least you are trying to request/redirect to). Read more here: http://www.codeigniter.com/user_guide/ge...uting.html