function to check customer is logged in or not in magento

<?php if($this->helper('customer')->isLoggedIn()) { ?>
   do some thing

<?php } else { ?>
 do some thing
<?php } ?>

how to get store id in magento

$storeId = Mage::app()->getStore($storeCode)->getId();

echo $storeId;

code to get categories and subcategories in magento ?

<--------------------

<div class="teamleftside1"> 
 <?php $_helper = Mage::helper('catalog/category') ?>
<?php $_categories = $_helper->getStoreCategories() ?>
<?php $currentCategory = Mage::registry('current_category') ?>
<?php if (count($_categories) > 0): ?>
    <ul>
        <?php foreach($_categories as $_category): ?>
            <li>
                <a href="<?php echo $_helper->getCategoryUrl($_category) ?>">
                    <?php echo $_category->getName() ?>
                </a>
                <?php $_category = Mage::getModel('catalog/category')->load($_category->getId()) ?>
                <?php $_subcategories = $_category->getChildrenCategories() ?>
                <?php if (count($_subcategories) > 0): ?>
                    <ul>
                        <?php foreach($_subcategories as $_subcategory): ?>
                            <li>
                                <a href="<?php echo $_helper->getCategoryUrl($_subcategory) ?>">
                                    <?php echo $_subcategory->getName() ?>
                                </a>
                            </li>
                        <?php endforeach; ?>
                    </ul>
                <?php endif; ?>
            </li>
        <?php endforeach; ?>
    </ul>
<?php endif; ?>


</div>
--------------------------->

How to call static block in the magento files ?

<?php echo $this->getLayout()->createBlock('cms/block')->setBlockId('block_id')->toHtml() ?>

where
block_id = the id which you given in the admin for the static block