This is a short guide how to add a widget on your screens.
First of all Its a widget, its not an application.
Long click on one of your screens until a popup menu appears,
(make sure there is available empty space for the widget) then choose widgets
and then scroll down until you see the clock and select it.
It will appear on your screen.
or checkout this video which is very nice
If you still have questions please contact me any time.