If you're trying to display associated blog posts on the Magento category page, this isn't possible. At the time of writing, associating a blog post with a Magento category is just a quick way to associate that post with all of the products in the category.
I will be working on an update in the future that will allow you to show associations on the category page, but currently this would require some custom development on your part. To do this, you would need to query the database to extract the post/category relationships and then load a post collection based on that.