if you need to get a list of blog post categories you can simply use this code:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16  | {category show="list" assign_to="categories"}
<div class="box">
    <div class="sidebar_header">
        <h4>Categories</h4>
    </div>
 
    <ul class="sidebar_menu">
        <ul>
        {foreach $categories.data as $cat}
            <li class="cat-item cat-item-{$cat.cat_ID} cat-{$cat.slug} {if $cat.slug == $query.category_name}active{/if}">
                <a href="{$cat.permalink}" title="{$cat.description}">{$cat.name}</a> ({$cat.count})
            </li>
        {/foreach}
        </ul>
    </ul>
</div> | 
{category show="list" assign_to="categories"}
<div class="box">
    <div class="sidebar_header">
        <h4>Categories</h4>
    </div>
    <ul class="sidebar_menu">
        <ul>
        {foreach $categories.data as $cat}
            <li class="cat-item cat-item-{$cat.cat_ID} cat-{$cat.slug} {if $cat.slug == $query.category_name}active{/if}">
                <a href="{$cat.permalink}" title="{$cat.description}">{$cat.name}</a> ({$cat.count})
            </li>
        {/foreach}
        </ul>
    </ul>
</div>