app/etc/modules/Nat_Products.xml
  
<?xml version="1.0" encoding="UTF-8"?>
<config>
    <modules>
        <Nat_Products>
            <active>true</active>
            <codePool>local</codePool>
        </Nat_Products>
    </modules>
</config>

  =====
 
 app/code/local/Nat/Products/etc/config.xml

<?xml version="1.0" encoding="UTF-8"?>
<config>    
    <modules>
        <Nat_Products>
            <version>0.1.0</version>
        </Nat_Products>
    </modules>
    
    <global>
        <models>
            <nat_products>
                <class>Nat_Products_Model</class>
            </nat_products>
        </models>
    </global>        
    
    <frontend>
        <routers>
            <addproduct>
                <use>standard</use>
                <args>
                    <module>Nat_Products</module>
                    <frontName>addproduct</frontName>
                </args>
            </addproduct>
        </routers>  
    </frontend>    
</config> 

app/code/local/Nat/Products/controllers/IndexController.php

<?php

class Nat_Products_IndexController extends Mage_Core_Controller_Front_Action {
public function indexAction() {

    echo 'Hello World from ' . __CLASS__ . "<br\>";  

    $product = Mage::getModel("products/addproduct");  // returns false  
    echo $product->hello();  
}  

}

=====

app/code/local/Nat/Products/Model/Addproduct.php

<?php
class Nat_Products_Model_Addproduct extends Mage_Core_Model_Abstract
{

public function hello()  
{  
    return "hello world from " .__CLASS__;  
}  

}

Hello World from Nat_Products_IndexController
( ! ) Fatal error: Call to a member function hello() on a non-object in maglocal.com\app\code\local\Nat\Products\controllers\IndexController.php on line 9

app/etc/modules/Nat_Products.xml

<?xml version="1.0" encoding="UTF-8"?>  
<config>  
    <modules>  
        <Nat_Products>  
            <active>true</active>  
            <codePool>local</codePool>  
        </Nat_Products>  
    </modules>  
</config>

app/code/local/Nat/Products/etc/config.xml

<?xml version="1.0" encoding="UTF-8"? >  
<config >      
    <modules >  
        <Nat_Products >  
            <version >0.1.0</version >  
        </Nat_Products >  
    </modules >  
      
    <global >  
        <models >  
            <nat_products >  
                <class >Nat_Products_Model</class >  
            </nat_products >  
        </models >  
    </global >          
      
    <frontend >  
        <routers >  
            <addproduct >  
                <use >standard</use >  
                <args >  
                    <module >Nat_Products</module >  
                    <frontName >addproduct</frontName >  
                </args >  
            </addproduct >  
        </routers >    
    </frontend >      
</config >   

=====

app/code/local/Nat/Products/controllers/IndexController.php

<?php  
  
class Nat_Products_IndexController extends Mage_Core_Controller_Front_Action {  
    public function indexAction() {  
  
        echo 'Hello World from ' . __CLASS__ . "<br\>";  
  
        $product = Mage::getModel("products/addproduct");  // returns false  
        echo $product->hello();  
    }  
} 

=====

app/code/local/Nat/Products/Model/Addproduct.php

<?php  
class Nat_Products_Model_Addproduct extends Mage_Core_Model_Abstract  
{  
  
    public function hello()  
    {  
        return "hello world from " .__CLASS__;  
    }  
  
}  

Hello World from Nat_Products_IndexController ( ! ) Fatal error: Call to a member function hello() on a non-object in maglocal.com\app\code\local\Nat\Products\controllers\IndexController.php on line 9