There are many plugin which allows you to display related blog posts in WordPress. This tutorial is on a different kind of related posts plugin which allows you to select the taxonomy type and it shows related posts only from that particular taxonomy given by you. With this plugin you can set related posts display by taxonomies like tags, categories and other custom taxonomies created by you.
Simply install and activate this lightweight plugin called Related Posts By Taxonomy. After activation visit your admin area Dashboard -> Appearance -> Widgets page and drag its widget to your sidebar and set the options like you can you can select a taxonomy to display related posts from, you can select posts types to include, number of related posts to show etc as shown in the given screenshot.