i am new in magento i want to add a category landing page my code is this but it show null

Question

<?php $_categories=$this->getCurrentChildCategories()?>
<?php $_collectionSize=count($_categories); ?>
<div>
<?php $i=0; foreach($_categories as $_category): ?>
<?php $layer = Mage::getSingleton('catalog/layer');
$layer->setCurrentCategory(Mage::getModel('catalog/navigation')->load($_category->getId()));
$helper = Mage::helper('catalog/navigation');
?>
<div>
<?php $_img=$this->getCurrentCategory()->getImageUrl()?>
<?php if($_img): ?>
</div>
<a href="<?php echo $helper->getCategoryUrl($_category);?>">
<img src="<?php echo $_img?>" title <?php echo $_category -> getName() ?> "/>
</a>
</div>
<?php endif; ?>
<div>
<a href="<?php echo $_category->getURL()?>" title="<?php echo $this->htmlEscape($_category->getName())?> ">
<?php echo $this->htmlEscape($_category->getName())?>
</a>
</div>
</div>
<?php $i++;
endforeach;
 ?>

</div>