Noir includes support for the great and popular plugin “Post Views Counter” so you can display posts that have the most views. When enabled the custom Popular Posts widget and the Footer posts (Trending Posts) will order by the most views. When the plugin is disabled these will be ordered by comment count.
Using The Widget
Simply go to Appearance > Widgets and drag the widget over to your sidebar.
Footer Trending Posts
Log into WordPress and go to Appearance > Customize > General Theme Settings > Footer Posts to set things up and or disable this section.