How to put my adsense code in this php code ?

Hi there,

I just upload new theme, and want to put my adsense pub-ID there, here’s the code they show me :
<!– Ad start –>
<div class=”sidebar_ads”><img src=”<?php bloginfo(‘stylesheet_directory’); ?>/images/180×150.gif” width=”180″ height=”150″ alt=”AD” /></div>
<!– Ad end –>

I want to place it in sidebar, since at first its only on .jpg mode, and i want to make it on by placing my code there so the link will work.

They told me to change it by myself, but i don’t know anything about .php. So i will be very grateful if someone could help me with this.

Thank you.