Include a block in sidebar – Magento

<reference name="left">
            <block type="catalog/navigation" name="catalog.leftnav" template="catalog/navigation/left_nav.phtml" />
</reference>
Please create file with the given name "left_nav.phtml " and put it in the corresponding location
eg : /app/design/frontend/your_package/yourtheme/template/catalog/navigation/left_nav.phtml