This is a simple widget like others to show your most popular posts based on views of your post. Put it in any of your widget area from your WordPress dashboard and the it will automatically show 5 most popular posts which will be visited most after the activation of the widget.So, after activation of the widget, visit a post of your website and see, it will show below the popular post title.
Install plugin from Plugin-> add new -> upload plugin -> PopularPostWidgetwithThumbnail.zip
Use widget go to Appearance -> widgets > Popular Post Widget with Thumbnail
Initial front-end view of popular posts.