Follow intallation guide per your link above,
5. Put <?php similar_posts(); ?> at the place in your theme files where you want the list of similar posts to appear. Lorelle on WordPress has a good guide to modifying themes for plugins.
If you are averse to editing template files you can also place the post listing automatically either as a widget in the sidebar of your widget-aware theme or after each post (from the plugin’s Placement submenu).
6. Use the admin Settings|Similar Posts pages to set all the available options. Alternatively, the options can be overridden by passing a parameter to the similar_posts template tag.
Usage and Options
The configuration page will help you to set up the plugin to your satisfaction.
