The plugin enables any user to modify the default order by which posts are ordered when they are displayed on any page of their blog.
The previous version of the plugin did not properly account for the first-time usage of the plugin settings. In other words, you have to visit the custom post order manangement page for the first time, in order for the plugin to initialize its variables. However, this problem was fixed in 1.1. Downloading the new version of the plugin will fix this error.
This plugin adds a filter to the "posts_orderby" event which is used whenever posts are being displayed on your blog. This means that to use it, all you have to do is save the custom post order options and you'll be able to see a different order of the posts displayed anywhere in your blog.
The plugin was either not activated for your blog, or the page that you are on does not display posts.