Hi,
First, you'll need to upload the icons to the /wp-content/themes/propulsion/images/layout/ folder using FTP. After you've done that open footer.php template located in the theme directory and find this line:
<li class='rss'><a href="<?php avia_option('feedburner',get_bloginfo('rss2_url')); ?>"><?php _e('Subscribe to our RSS Feed', 'avia_framework')?></a></li>
Now you'll want to add your links before or after the link above like this:
<li class='rss'><a href="<?php avia_option('feedburner',get_bloginfo('rss2_url')); ?>"><?php _e('Subscribe to our RSS Feed', 'avia_framework')?></a></li><li class='youtube'><a href="http://www.youtube.com/my-url>"><img src="<?php bloginfo('template_directory'); ?>/images/layout/name-of-your-file.png" /></a></li>
Just copy/paste this line for each link just be sure to change the class name, URL and "name-of-your-file.png" to match each link. (Note: The class name is there just in case you want to do some styling in the CSS.)
<li class='youtube'><a href="http://www.youtube.com/my-url>"><img src="<?php bloginfo('template_directory'); ?>/images/layout/name-of-your-file.png" /></a></li>
Regards,
Mya