Widgets are tools that you can add to your site to customize it and/or allow for additional features. There are a number of them available through U.OSU and this help article will show you how to activate them.
Some plugins include additional widgets. For example, the Jetpack plugin contains a number of widgets that you can activate: Sharing, Slideshows, Title Galleries, Widget Visibility and more. The Jetpack widgets help you display your content; however, the plugin allows you to create them.
Once activated, Widget Visibility - a Jetpack widget - adds a field on all widgets to specify which widgets appear on which pages of your site. See Jetpack for details about how to set up and activate the Jetpack plugin and widgets.