Feature highlighting is a great way to encourage interaction with your map. Features are highlighted when the mouse cursor is placed above them, the user can then click on the highlight in order to open up the popup containing information about the feature.
Simply move the mouse around the map and see the items highlighted. As the highlight feature uses browser side rendering, it's limited to layers with fewer than 1000 features in order to ensure performance.
From the administration area of your map this tool can be activated from the toolbox panel in the administration toolbar. See the following section in the documentation for more details.