Can’t get the Simple Post Thumbnails plugin to work

Hi, I’ve been trying to figure out how to get this plug-in to work with custom thumbnails and I’m basically lost.

I searched this blog and found that I’m supposed to insert the code below somewhere, but the problem is, I don’t have any clue where. Can someone help me out with this, please?

“><img alt=”<?php the_title(); ?>” src=”<?php echo p75GetThumbnail($post->ID, null, null); ?>” style=”float:left;margin:0 10px 0 0;” border=”0″ />