Widget is a way of showing content in WordPress sidebars. Adding widgets to your blog is a great way of showing featured content and other features like services, products and related content.
Recent articles, categories, menus, subscription forms and all type of related information can be displayed in sidebars using widgets.
Widget locations vary from theme to theme. The most popular location to add widgets is right sidebar but you can add widgets to left sidebar, footer, header and other locations defined in your theme.
From your dashboard, go to Appearance > Widgets to see all the available widgets