To copy another user's widget to your dashboard, click on the Dashboard icon, and then where it says 'Widgets in this Layout' click the plus button:
A window will appear. Choose 'Add existing widget'. At the bottom of the list will be the 'Shared' category. Choose the appropriate widget.
Tip: to share one of your custom widgets with others (so that it appears under 'shared' in their accounts), click on the three dots next to the widget and select 'Share'.