Where in to place the php code of a plugin?

PHP Code:
<?php if(!defined('IN_GS')){ die('you cannot load this page directly.'); }
/****************************************************
*
* @File:             sidebar.inc.php
* @Package:        GetSimple
* @Action:        Innovation theme for GetSimple CMS
*
*****************************************************/
?><aside id="sidebar">

    <div class="section" id="socialmedia" >
        <h2>Connect</h2>
        <div class="icons">
            
            <!-- Social Media URLs are set within this theme's settings plugin -->
            <?php if (defined('FACEBOOK')) { ?>
                <a href="<?php echo FACEBOOK; ?>"><img src="<?php get_theme_url(); ?>/assets/images/facebook.png" /></a>
            <?php } ?>
            <?php if (defined('TWITTER')) { ?>
                <a href="<?php echo TWITTER; ?>"><img src="<?php get_theme_url(); ?>/assets/images/twitter.png" /></a>
            <?php } ?>
            <?php if (defined('LINKEDIN')) { ?>
                <a href="<?php echo LINKEDIN; ?>"><img src="<?php get_theme_url(); ?>/assets/images/linkedin.png" /></a>
            <?php } ?>
            
            <img src="<?php get_theme_url(); ?>/assets/images/break.png" />
            
            <!-- addthis popup - you can add your username if you want analytics: http://www.addthis.com/help/customizing-addthis -->
            <div class="addthis_toolbox" style="display:inline;width:24px;" >
                <a href="//www.addthis.com/bookmark.php?v=250" class="addthis_button_compact"><img src="<?php get_theme_url(); ?>/assets/images/share.png" /></a><br>
                        </div>
            <script type="text/javascript" src="//s7.addthis.com/js/250/addthis_widget.js"></script>
        </div>
    </div>
        
    <!-- wrap each sidebar section like this -->
    <div class="section">
        <?php get_component('sidebar');    ?>
    
    
    </div>

       [b] <div>
        <?php get_search_form(array('slug'=>'search', 'showTags'=>0)); ?>
        </div>[/b]
</aside>