Cara Input

 
<form action="<?php site_url('form/submit');?>" method="post">
   <input type="text" name="f_name">
   <input type="submit" name="Submit">
</form>

class Mymodel extends Model{
    function do_something($param){
        //Do something with param
    }
}

class Form extends Controller{
    function submit(){
        $fname  = $this->input->post('f_name');
        $this->load->database();
        $this->load->model('mymodel');
        $this->mymodel->do_something($fname);
        // do something
    }
}