If the user has been given the permission to edit their dashboard, the Edit Mode button will be available on the top right of their dashboard.  

Clicking Edit Mode will allow you to review the available dashboard widgets (orange section) and click and drag them to the dashboard (blue section).  Newly added and existing widgets can be re-arranged by click and dragging to the preferred order.

Once the dashboard has been customised to your linking, click Save Edits to lock in the changes.

If you need to reset the dashboard back to the defaults, a customised dashboards will display the green Set Defaults button to allow you to revert to the default dashboard.