This function lets you preview the widget's functionality or the entire dashboard's content at runtime. 

You need to go to the Administration > Dashboard Widgets page. 

The Dashboard Widgets UI is shown below. The widgets are organized in a table with columns for display name, description, and validation status. Use the Search box to filter the list.  

Choose the dashboard widget from the list, then click the View > Preview menu option. 

The Widget UI Preview pop-up displays the widget's functionality as follows. Click the Close button to proceed.