Hi,

I installed the Wordpress-PostRatings Plugin.

But in the frontend you can´t see anything.

The user should have the possibility to rate a post. This would be displayed by Google as Rich Snippet...

Do you know what to do?

In the installation guide of the Plugin it says:
Open wp-content/themes/<YOUR THEME NAME>/index.php
You may place it in archive.php, single.php, post.php or page.php also.
Find: <?php while (have_posts()) : the_post(); ?>
Add Anywhere Below It (The Place You Want The Ratings To Show): <?php if(function_exists('the_ratings')) { the_ratings(); } ?>

The problem is:
Can´t find the right code: <?php while (have_posts()) : the_post(); ?>

Instead of editing theme files you might try putting a new widget area in one of the areas in Edit Post/Page Info Options. Then use a php aware text widget to add the code the plugin is giving you. Alternatively you can just use the shortcode on the posts you want to allow people to rate.

I found a good functioning Plugin without problems:

GD Star Rating.

You can see the results in my Blog:
http://geistreich78.info/