class User extends CI_Controller{

function login(){


    $this->load->helper('form');
    $this->load->library('form_validation');

    $this->form_validation->set_rules('username', 'username', 'required');
    $this->form_validation->set_rules('password', 'password', 'required');
    $this->form_validation->set_error_delimiters('<em>','</em>');

    if($this->input->post('weiter')){

        if($this->form_validation->run()){
            echo "okay";

        }
    }else{
        $this->load->view("templates/header");
        $this->load->view("user/login");
        $this->load->view("templates/footer");
    }





}

$route['user/login'] = 'user/login';

<?php echo form_open("user/login");?>
<table>

    <tr>
        <td><label for="username">Username</label></td>
        <td><input type="text" name="username"></td>
    </tr>
    <tr>
        <td><label for="password">Passwort</label></td>
        <td><input type="password" name="password"></td>
    </tr>
    <tr>
        <td><input type="submit" name="weiter"></td>
        <td></td>
    </tr>
</table>

<form method="post">
<table>

    <tr>
        <td><label for="username">Username</label></td>
        <td><input type="text" name="username"></td>
    </tr>
    <tr>
        <td><label for="password">Passwort</label></td>
        <td><input type="password" name="password"></td>
    </tr>
    <tr>
        <td><input type="submit" name="weiter"></td>
        <td></td>
    </tr>
</table>
</form>

<?php
    echo form_open(base_url('user/login'));
   ?>
   <table>

<tr>
    <td><label for="username">Username</label></td>
    <td><input type="text" name="username"></td>
</tr>
<tr>
    <td><label for="password">Passwort</label></td>
    <td><input type="password" name="password"></td>
</tr>
<tr>
    <td><input type="submit" name="weiter"></td>
    <td></td>
    </tr>
 </table>
     <?php echo form_close();
       ?>